Add reST script to generate x265 user manual

--HG--
branch : stable
api: add param.bRepeatHeaders - insert stream headers in each keyframe NAL

This is apparently useful for raw stream formats
Merge with stable
rest: add Makefile for generating HTML from reST, cleanup some nits
rest: use comma to separate short and long options

This looks better, and fixes cross referencing
rest: fix csv logging descripion, move debug options to the end
rest: large cleanup of CLI opt docs
rest: improve CLI docs, fix some wrong descriptions, moar better

I've moved --weightp and --refs to the ME section since they have no bearing
on slice decision and lots of impact on motion search.  Some new options are
still missing, will add those in a later commit