dawgdic: new package

The dawgdic package provides object files and utilities for building
and accessing directed acyclical word graph (DAWG) dictionaries.

This version of the patch uses the updated GitHub dawgdic repo instead
of the Google Code repo used in the previous version of this patch.

[Thomas:
  - use the github macro for <pkg>_SITE
  - remove <pkg>_SITE_METHOD, useless once you use the github macro
    for <pkg>_SITE
  - fix the license, it is BSD-3c and not GPLv3
  - remove commented <pkg>_SITE in the .mk file
  - add missing dependency on C++.]

Signed-off-by: Jonathan Ben Avraham <yba@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>