API changes, most recent first:
+2017-03-xx - xxxxxxx - lavu 55.35.0 - hwcontext.h
+ Add AV_HWDEVICE_TYPE_NONE, av_hwdevice_find_type_by_name(),
+ av_hwdevice_get_type_name() and av_hwdevice_iterate_types().
+
2017-03-xx - xxxxxxx - lavu 55.34.0 - hwcontext.h
Add av_hwdevice_ctx_create_derived().