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.
