flvdec: Support HM10.0-based Strongene HEVC demuxing.
hevc: Search start code in decode_nal_units().

User may cut off a weird position and send a packet from there.
This avoids returning as invalid data immediately.
hevc_parser: Set pict_type, key_frame and output_picture_number.

Remove key_frame setting in hevc_find_frame_end().
key_frame setting in parse_nal_units() is better since hevc_find_frame_end() is not invoked when PARSER_FLAG_COMPLETE_FRAMES is set.
hevc_parser: Support bitstream encapsulated as 14496-15 format.
hevc: Set chroma_sample_location of AVCodecContext.
h264_ps: Set chroma_sample_location appropriately if chroma location info is absent.