API changes, most recent first:
+2017-03-30 - xxxxxxx - lavu 55.53.100 / 55.27.0 - hwcontext.h
+ Add av_hwframe_map() and associated AV_HWFRAME_MAP_* flags.
+ Add av_hwframe_ctx_create_derived().
+
2017-03-xx - xxxxxxx - lavu 55.52.100 - avutil.h
add av_fourcc_make_string() function and av_fourcc2str() macro to replace
av_get_codec_tag_string() from lavc.