output example: set the stream timebase

This is required by the new API.
output example: convert audio to the format supported by the encoder
hevcdsp: remove an unneeded variable in the loop filter

beta0 and beta1 will always be the same
hevc: SSE2 and SSSE3 loop filters

Additional contributions by James Almer <jamrial@gmail.com>,
Carl Eugen Hoyos <cehoyos@ag.or.at>, Fiona Glaser <fiona@x264.com> and
Anton Khirnov <anton@khirnov.net>

Signed-off-by: Anton Khirnov <anton@khirnov.net>