Update to v0.4.2
Update to v0.4.2

This version contains a grab bag of changes I've made.

The big reason to push a new version is switching to a dual MIT/Apache license,
per the request of a giant robot.

Changelog:

* Added generators for basic windowing functions.
* Implemented a couple more iterator traits for ringbuf.
* Iterative improvements to the Error class.
* Removed or documented existing unwraps as approriate.
* Expanded the fields covered by the MIDI message enum.
* Cleanup of some documentation.
* Dependency updates.

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