support for auto detect of alsa sample format
support of S32_LE
optimisation for 100% volume case
wait for 1 sec worth of decoded samples before starting 172/192k streams (equivalent of output_threshold 100)
add support of usb output devices which become unavailable and then return later
- by waiting for the same device name to become available again
- requires device to be available at startup so the max sample rate can be found
add ability to fallback to plughw: for hw: device if resampling is required
protect against corrupt sample rate (if 7.8 server used with 7.7 squeezeplay for pcm)
experimental cpu randomisation

CPU load of jive_alsa occurs very regularly as snd_pcm_wait wakes after every interrupt for more data
attempt to randomise this by calculating wait period and using usleep instead, requires period count of >= 3
enabled by adding 100 to period count
ignore tuned buffer values when using plug layer

snd_pcm_close can crash when switching if pcm is opened with large buffer time values when using plug layer
avoid this by hard coding touch defult buffer values for use with low samplerate streams requring sample rate conversion
Merge branch '7.8' of https://github.com/triode/squeezeplay into 7.8

Conflicts:
	src/squeezeplay/src/audio/decode/decode_alsa_backend.c