Improve events documentation by adding cross references,
sub-titles and other markup elements.
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

Move the v4l2 event-specific text from v4l2-framework.rst
to v4l2-event.rst. That helps to keep the text together with
the functions it describes, and makes easier to identify
documentation gaps.
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

Sphinx produce a 1:1 mapping between a rst file and an html file.

So, we need to split the kernel-doc tags on multiple documents.

A side effect is that we're now having a better name for each
section of the kAPI documentation.
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>