move vorbis, lame and flac audio encoders to add-ons
fixed: don't crash on (too) early calls
refactor AEChannelInfo and AEAudioFormat enums

put in a separate file for exposure to add-ons
add preprocessor definition for identifying add-on builds
add support for audio decoder addons
move modplug to addon
remove YM/Stsound

now an add-on
remove nosefart

now an add-on
remove flacdecoder

now an add-on
remove sidplay

now an add-on
remove ogg/vorbis decoder

now an add-on
remove files now in add-ons
add enable/disable switch for tests
now depends on cpluff
set build type in add-on builds
remove vgmstream

now an add-on
remove timidity

now an add-on
remove snesapu

now an add-on
remove xbadpcm codec

supported in ffmpeg
remove asap

now an add-on