Import all function documentations, return code reference
into the header files, as doc comments,
in the hopes of moving the CAref.html manual to docs.epics-controls.org,
which will be done in a later PR.
Also added doc comments to some other low-hanging fruits,
for example when plain comments where near, or when it was obvious to do so.
Adds the build target 'sphinx' for manual Sphinx runs, and
installs the output of that under $(INSTALL_HTML)/readthedocs
Adjusted some Sphinx config parameters and titles.
That .pod file will now be converted to .html using the same style as
the individual local documents that it links to.
The dbdToHtml output files now include a header and footer that link to
the ComponentReference.html file (they started pointing to the original
RecordReference.html but that was broken on most people's builds because
we weren't converting that from the original Markdown version).
This commit also adjusts documentation/Makefile to use the build system
properly, and reorders the Doxygen main page index.
