FS-7505: clean up and support multiple formats to same extensions {modname=mod_vlc}rtmp://foo.com/flvplayback also move [/tmp]file to be {spool_path=/tmp}

Tested with libav 11.3
./configure --prefix=/opt/av --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --host-cflags= --host-ldflags= --enable-libx264 --enable-libmp3lame --enable-libvorbis --enable-libvpx --enable-libfaac --enable-libspeex --enable-nonfree --enable-vda

WIP av file interface, kind of works, need further tweak & cleanup

made it like a codec mod so we can share the same code in case opus is fully supported in webm
add -lvorbis -lvorbisenc to Makefile
the audio is still completely silence, hope we can find out why

use SWITCH_RTP_MAX_BUF_LEN for video
timestamp has to times 1000 or it too short
neither VLC nor Chrome plays it because they don't support OPUS,
but you can use `ffmpeg -i a.webm b.webm`