docs: Major clean up of doxygen generated core API documentation

docs: Major clean up of doxygen generated core API documentation

To make the API documentation usable (again):

  - Rename to "FreeSWITCH API Documentation"

  - Remove all external INPUT paths, only scan FreeSWITCH core sources

  - Only parse a sane subset of files: *.c *.cc *.cpp *.h *.hh *.hxx
    (don't care about any python / whatever files for now)

  - Exclude modules (seriously, all the mod_java / mod_managed stuff
    turned it into an unusable mess. You need API docs of modules? Add separate doxygen
    configurations for them (or specific ones))

  - Include src/mod in example search path (for @include etc.), add C/C++
    patterns.

  - Set up PREDEFINED to fix the massive clusterf*ck that was caused by
    SWITCH_DECLARE() and friends.

<End Of Rant>

Signed-off-by: Stefan Knoblich <s.knoblich@axsentis.de>