Improve documentation of WP_Rewrite. Fixes #19897.

In particular WP_Rewrite::$front, WP_Rewrite::$root, WP_Rewrite::$use_verbose_page_rules and WP_Rewrite::generate_rewrite_rules(). As well as some code indentation prettification.


git-svn-id: https://core.svn.wordpress.org/trunk@19752 1a063a9b-81f0-0310-95a4-ce76da25c4cd