Added links to default widget in forms.fields documentation

.. class:: BooleanField(**kwargs)

    * Default widget: ``CheckboxInput``

    * Default widget: :class:`CheckboxInput`

    * Empty value: ``False``

    * Normalizes to: A Python ``True`` or ``False`` value.

    * Validates that the value is ``True`` (e.g. the check box is checked) if

.. class:: CharField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``''`` (an empty string)

    * Normalizes to: A Unicode object.

    * Validates ``max_length`` or ``min_length``, if they are provided.

.. class:: ChoiceField(**kwargs)

    * Default widget: ``Select``

    * Default widget: :class:`Select`

    * Empty value: ``''`` (an empty string)

    * Normalizes to: A Unicode object.

    * Validates that the given value exists in the list of choices.

    Just like a :class:`ChoiceField`, except :class:`TypedChoiceField` takes two

    extra arguments, ``coerce`` and ``empty_value``.

    * Default widget: ``Select``

    * Default widget: :class:`Select`

    * Empty value: Whatever you've given as ``empty_value``

    * Normalizes to: A value of the type provided by the ``coerce`` argument.

    * Validates that the given value exists in the list of choices and can be

.. class:: DateField(**kwargs)

    * Default widget: ``DateInput``

    * Default widget: :class:`DateInput`

    * Empty value: ``None``

    * Normalizes to: A Python ``datetime.date`` object.

    * Validates that the given value is either a ``datetime.date``,

.. class:: DateTimeField(**kwargs)

    * Default widget: ``DateTimeInput``

    * Default widget: :class:`DateTimeInput`

    * Empty value: ``None``

    * Normalizes to: A Python ``datetime.datetime`` object.

    * Validates that the given value is either a ``datetime.datetime``,

.. class:: DecimalField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``None``

    * Normalizes to: A Python ``decimal``.

    * Validates that the given value is a decimal. Leading and trailing

.. class:: EmailField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``''`` (an empty string)

    * Normalizes to: A Unicode object.

    * Validates that the given value is a valid email address, using a

.. class:: FileField(**kwargs)

    * Default widget: ``ClearableFileInput``

    * Default widget: :class:`ClearableFileInput`

    * Empty value: ``None``

    * Normalizes to: An ``UploadedFile`` object that wraps the file content

      and file name into a single object.

.. class:: FilePathField(**kwargs)

    * Default widget: ``Select``

    * Default widget: :class:`Select`

    * Empty value: ``None``

    * Normalizes to: A unicode object

    * Validates that the selected choice exists in the list of choices.

.. class:: FloatField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``None``

    * Normalizes to: A Python float.

    * Validates that the given value is an float. Leading and trailing

.. class:: ImageField(**kwargs)

    * Default widget: ``ClearableFileInput``

    * Default widget: :class:`ClearableFileInput`

    * Empty value: ``None``

    * Normalizes to: An ``UploadedFile`` object that wraps the file content

      and file name into a single object.

.. class:: IntegerField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``None``

    * Normalizes to: A Python integer or long integer.

    * Validates that the given value is an integer. Leading and trailing

.. class:: IPAddressField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``''`` (an empty string)

    * Normalizes to: A Unicode object.

    * Validates that the given value is a valid IPv4 address, using a regular

    A field containing either an IPv4 or an IPv6 address.

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``''`` (an empty string)

    * Normalizes to: A Unicode object. IPv6 addresses are

      normalized as described below.

.. class:: MultipleChoiceField(**kwargs)

    * Default widget: ``SelectMultiple``

    * Default widget: :class:`SelectMultiple`

    * Empty value: ``[]`` (an empty list)

    * Normalizes to: A list of Unicode objects.

    * Validates that every value in the given list of values exists in the list

    Just like a :class:`MultipleChoiceField`, except :class:`TypedMultipleChoiceField`

    takes two extra arguments, ``coerce`` and ``empty_value``.

    * Default widget: ``SelectMultiple``

    * Default widget: :class:`SelectMultiple`

    * Empty value: Whatever you've given as ``empty_value``

    * Normalizes to: A list of values of the type provided by the ``coerce``

      argument.

.. class:: NullBooleanField(**kwargs)

    * Default widget: ``NullBooleanSelect``

    * Default widget: :class:`NullBooleanSelect`

    * Empty value: ``None``

    * Normalizes to: A Python ``True``, ``False`` or ``None`` value.

    * Validates nothing (i.e., it never raises a ``ValidationError``).

.. class:: RegexField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``''`` (an empty string)

    * Normalizes to: A Unicode object.

    * Validates that the given value matches against a certain regular

.. class:: SlugField(**kwargs)

   * Default widget: ``TextInput``

   * Default widget: :class:`TextInput`

   * Empty value: ``''`` (an empty string)

   * Normalizes to: A Unicode object.

   * Validates that the given value contains only letters, numbers,

.. class:: TimeField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``None``

    * Normalizes to: A Python ``datetime.time`` object.

    * Validates that the given value is either a ``datetime.time`` or string

.. class:: URLField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``''`` (an empty string)

    * Normalizes to: A Unicode object.

    * Validates that the given value is a valid URL.

.. class:: ComboField(**kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``''`` (an empty string)

    * Normalizes to: A Unicode object.

    * Validates that the given value against each of the fields specified

.. class:: MultiValueField(fields=(), **kwargs)

    * Default widget: ``TextInput``

    * Default widget: :class:`TextInput`

    * Empty value: ``''`` (an empty string)

    * Normalizes to: the type returned by the ``compress`` method of the subclass.

    * Validates that the given value against each of the fields specified

.. class:: SplitDateTimeField(**kwargs)

    * Default widget: ``SplitDateTimeWidget``

    * Default widget: :class:`SplitDateTimeWidget`

    * Empty value: ``None``

    * Normalizes to: A Python ``datetime.datetime`` object.

    * Validates that the given value is a ``datetime.datetime`` or string

.. class:: ModelChoiceField(**kwargs)

    * Default widget: ``Select``

    * Default widget: :class:`Select`

    * Empty value: ``None``

    * Normalizes to: A model instance.

    * Validates that the given id exists in the queryset.

.. class:: ModelMultipleChoiceField(**kwargs)

    * Default widget: ``SelectMultiple``

    * Default widget: :class:`SelectMultiple`

    * Empty value: An empty ``QuerySet`` (self.queryset.none())

    * Normalizes to: A ``QuerySet`` of model instances.

    * Validates that every id in the given list of values exists in the