test.py: add ScaleTest

Add ScaleTest class with basic tests cases for
LogScale and HarmonicScale.
splat.scales.Scale: add abs_cycles to use absolute notation

When Scale.abs_cycles is set to True, the notes naming convention
uses absolute cycle numbers which is independent of the key.  The
pitch note is in cycle 4 (so A4 is 440 Hz with default
parameters).  Defaults to False.
doc: scales: add absolute notation + review
test.py: ScaleTest: add cases for relative notation
_splat.c: define audio_formats

* add _splat.audio_formats
* import _splat.audio_formats into splat
* remove duplicate audio_formats in splat/__init__.py