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.
decoder, asap: Fix memory leak.
no-glib: Rule out g_build_filename.

There may still be some g_free/free mismatches, you're warned.
no-glib: Rule out g_strdup, g_strndup, g_new, g_malloc.
update: Correctly deal with NULL path
no-glib: Rule out several G_GNUC macros.
no-glib: Delete G_GNUC_CONST
no-glib: Clear G_GNUC_UNUSED
headers: Retire gcc.h.

1) I don't use funny version checks and #pragmas to workaround false
postive gcc warning. I just ignore them.

2) I don't use gcc_nonnull. You gonna have null guard in your code any
way.

3) Why is there a gcc_packed? I deleted it. May cause ABI breakage
though.
no-glib: Remove as much g_free as I can.

The others might require some additional code to remove.
no-glib: Replace G_UNLIKELY/LIKELY
conf: Correctly handle NULL config string.
path: Handle conversion failure
no-glib: Clear a few more g_free.
TODO
util, list: Clear up list.h a bit

To allow C++ source files to use it as well.
gcc.h: Remove a left-over.
util, file_util: rename build_filename to build_db_filename.

Make it clear that this function is for building internal filenames.

Also accept NULL as first argument, and always use '/'.