ao_coreaudio: allow to use exclusive mode with lpcm
ao_coreaudio: redo stream/format selection
fix typo
renames
ao_coreaudio: report back the correct format
ao_coreaudio: simplify stream selection
ao_coreaudio: remove mixing mode disabling on device

Apparently this must be done on stream level as opposed to device level.
kAudioDevicePropertySupportsMixing is in the AudioHardwarDeprecated.h header
so it may disappear anyway.
ao_coreaudio: extend :list to show more informations

Makes it show mixable status of the stream and lists the virtual formats
available.
ao_coreaudio: try to set both virtual and physical formats
ao_coreaudio: initial support for bitperfect path