Missing bounds-checks for VUI Bitstream Restriction Syntax Elements

[wrv]

The VUI bitstream restriction syntax elements are not bounds checked: https://github.com/dholroyd/h264-reader/blob/master/src/nal/sps.rs#L803-L812

Expected bounds, according to Annex E.2.1 of the spec:

• max_bytes_per_pic_denom: [0, 16]
• max_bits_per_mb_denom: [0, 16]
• log2_max_mv_length_horizontal: [0, 15]
• log2_max_mv_length_vertical: [0, 15]
• max_num_reorder_frames: [0, max_dec_frame_buffering]
• max_dec_frame_buffering: [max_num_reorder_frames, MaxDpbFrames] where MaxDpbFrames is set by the Level