Improve doxygen comment.

Improve layout, add trailing '.' in function description, capitalize first letter of description, fix typo, turn \0 into \\0.
Move the detailled description after @defgroup so that it is taken into account.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1611252 13f79535-47bb-0310-9956-ffa450edef68