New ideas

* Got rid of the shabby editor, which, while very clever, wasn't ever going to feel quite right because of Tk's refresh-rate limitations combined with mass-vanilla-canvas-spam lag.
* Fixed various bugs.
* Changed loadfile behavior; loadfiles are now a Format 1 MIDI file, with each MIDI track corresponding to a given sequence.
* Added a tiny pseudo-API, to allow editor programs to send OSC commands that trigger Extrovert behaviors.
* Organized functions into multiple files, because poking around in a 2500-line file is super demoralizing.