tests/src/io/test-sink*: use source native samplerate
tests/src/io/test-sink*: improve, unify
src/tempo/tempo.c: novelty function default to specflux
src/io/source_apple_audio.c: do_multi do not write outside of matrix
src/io/sink_apple_audio.h: add do_multi, preset_samplerate, preset_channels, get_samplerate, and get_channels
src/io/sink_wavwrite.h: add do_multi, preset_samplerate, preset_channels, get_samplerate, and get_channels
src/io/sink_sndfile.h: add do_multi, preset_samplerate, preset_channels, get_samplerate, and get_channels
tests/src/io/test-sink_sndfile-multi.c: fix flags
tests/src/io/test-sink_wavwrite-multi.c: fix flags
src/io/sink.h: add do_multi, preset_samplerate, preset_channels, get_samplerate, and get_channels