rest: update introduction page, add more detail about software patents
cli: report input bit depth
y4m: support variable bit depth via CXXXpDD Y4MPEG header; ie: C420p10

ffmpeg's support for this is non-standard, so you must use -strict -1, aka:

ffmpeg -i vid.avi -pix_fmt yuv420p10le -strict -1 -f yuv4mpegpipe - | ./x265 - --y4m o.hevc

closes issue #53