First stab at reducing passing context as argument
Use multiple arity to clean up functions

- Allow things like note-on and note-off to take arguments that were previously hardcoded
Move up ctx-for to prevent complaints
Use params map for functions with more parameters
Unnecessary; was going to use this but didn't
optional key arguments, or default arguments
Bump version to 0.3.0 for release.

- This thread fixes #2
Merge pull request #3 from mathias/simplify_contexts

hum 0.3.0 release features