zlib: fix a misuse of ferror
decoder, ffmpeg: AVCODEC_MAX_AUDIO_FRAME_SIZE is deprecated.

It has been deprecated for a very long time now.

Also whoever wrote copy_interleave_frame must've been on drugs.
Add coding_style.

This file mostly concerns about those aspects of style that can't be
dealt with using tools like astyle.
input, soup: Retire libsoup support.

libcurl is more preferable.