Rework documentation storage/process

C/C documentation consists of API pages (mysql_real_connect, etc) and non-API pages ("Building and Installing", "Compatibility", etc). API pages directly correspond to man pages that are included in C/C source and binary packages.

Currently, the primary source of C/C documentation is github wiki. Periodically Georg clones the wiki repo, runs pandoc to convert .md files into .3 manpages and checks them into C/C repository.

Drawbacks:

• C/C repository stored generated files, not source files, as it should.
• manpages are not versioned, C/C 3.2 has manpages that describe 3.3 features.

If using an online-editable wiki is not a goal, we can move documentation to read-only github pages, as:

• put docs in a separate repo connector-c-docs
• convert all API pages to troff or, may be,
• convert all non-API pages to whatever, e.g. sphinx
• libmariadb will include connector-c-docs as a submodule or as ExternalProject
• 3.3 specific parts will be conditionally marked, so they could be skipped in 3.2
• sphinx and groff -Thtml will generated pages for online manual.

or

• all pages are in sphinx
• man pages are generated by sphinx
  • means, a builder have to have sphinx
  • source tarballs should have preprocessed manpages
• conditional output from sphinx? (may be using .. only:: directive?)