Add max_bit_rate to Stream

FFMPEG does not return a bit-rate for mpeg2 video streams. When this
happens you could fallback to the max_rate.

Libav however does return a bit-rate for mpeg2.

Tests added which handle differences in results between lib and ffmpeg.
Add width and height read properties to Stream.
Add codec profile to Stream
Add coded_height and coded_width to VideoStream

Some file specifications specify that the coded height and width needs
to vary from the picture resolution, so these are good parameters to
have available for QA type usage.
Add display_aspect_ratio to VideoStream
Add with-audio & language to generate_video

This will be used for tests that require a video & audio file.
Add language to Stream.

New language get property for Stream with tests.