Improvements to simpleHats.py

Add comments in simpleHats.py
Added bass drum in simpleHats.py
(They're not so simple anymore!!!)
Added midi to gitignore
Added Measure::addVoice
Added piano to arezzo.instruments
Added countOff in al_mid
Add arezzo.ToneCluster

ToneCluster::around is still incomplete
Add case in writer function to deal with toneclusters
Add pianoComp to basie
Add command line arguments in al_mid
New methods in Note

Add 8vb and 8va methods in Note

Add dynamic field in Note
Added testing
Made basie.pianoComp use chord inversions for a more natural sound
Get rid of print in al_mid
Add note dynamic in writer.py
Add command line arguments in build_and_play
Add emphasis on first beat in walking bass
Add examples