First version of EventBusParser

Seems to work; but we need more tests, of course!
Introduce BasicMatchEvent

Action context is some pesky thing; use a "delegating class" to capture what is
wanted from the context.

The existing BasicMatchEvent class only captures the context's .getMatch().
Rename "cleanup" package to "annotations"
Add an @Experimental annotation; annotate event classes with it
Javadoc for EventBusParser and BasicMatchEvent
More documentation for event bus parser
event package: add package-info.java

Meh. That is the first package-info in the whole project.
Tests for EventBusParser

Some tests, at least; not all of them, I am aware of that.