Doc overhaul and Notes is a new struct

See our new README.md for more.

Notes is now a new struct, not just a vector of Notes.

Added Notes, BPM, ms_per_tick

See the updated README.md !

Dropped Julia 0.5 support

Merge pull request #78 from yurivish/master

Fix some warnings & deprecations on 0.6

v0.1.0

• Dropped compatibility with Julia 0.3, moved straight ahead to 0.5.
• Functions now have proper docstrings
• Velocity 0 noteOn events are interpreted as noteOff