Increase default MIDI ticksPerQuarter

[TimFelixBeyer]

According to comments in the code, the default MIDI ticksPerQuarter is set to 1024 to avoid a limitation in midi.py, which is no longer used.
Therefore, I propose to set the ticksPerQuarter to 10080 which is the same value used for MusicXML divisions. This would allow exported MIDI to represent more durations exactly without quantization errors and without significant risk/downsides.
I have also updated all relevant tests.
Let me know what you think!

[coveralls]

Coverage: 93.104% (+8.0e-05%) from 93.104% when pulling 05548b0 on TimFelixBeyer:patch-6 into c20a4cd on cuthbertLab:master.

[mscuthbert]

Good idea. Compatibility with buggy versions of midi.py is no longer a consideration, agreed.

Can you explain why the note was changed from 128th note to double the duration? Is there a bug that emerged?

[TimFelixBeyer]

Sure, 1024 = 2^10, so we can represent even a 1/4096th note using integer ticks.
10080 = 2^5 * 3^2 * 5 * 7, so the smallest standard (1/2^n) note it can represent exactly is a 1/128th note.
The example effectively implemented a 3/256th note (dotted 128th), which would have required a non-integer tick.

I‘d advise against increasing the default ticksPerQuarter over 10080, as it is already on the high side for MIDI (typical range 120-960), and very high ticks may lead to compatibility problems with other libraries (craffel/pretty-midi#175)
Users can always override the default if they want more precision and want to represent tiny notes (3/256th) exactly.

[mscuthbert]

Thanks! Got it!