doc: update doxygen configuration

This was performed by executing: doxygen -u
Update copyright year
doc: update version number in doxygen config

Not sure whether that is actually used somewhere.
doc: use c as default sphinx role

This might fix the documentation build issue on readthedocs.org.
doc: enable C syntax highlighting by default
doc: fix a couple of API doc warnings

In restructured text double backquotes are used for inline literals.
vis: remove ae outer entire text object

Use :, which is a short hand for :0,$ instead.
vis: remove ie inner entire text object
vis: remove z> rightmost pairwise selection combinator
vis: remove z< leftmost pairwise selection combinator
vis: remove z- shorter pairwise selection combinator
vis: remove z+ longer pairwise selection combinator
vis: remove z& pairwise selection intersection
vis: remove z| pairwise union
vis: remove commented entries from default config
vis: use ~ instead of ! for selection complement

This seems more consistent with the typical set/bit operations.
vis: remove ~ as alias for g~
vis: remove window related aliases from default config
vis: remove special key aliases from default config

These can all be performed using home row keys.