fixed accidental commenting that caused non-restructured asigs to generate nothing in the macro
implemented Butterworth 2nd-order filters (low pass, high pass, band pass, band reject); based on Csound implementations of butterlp, butterhp, butterbp, butterbr
formatting
made add-events take in list of standard events, do the wrapping with engine-events
fixed bad type hints
initial outline for document about unit generators
initial work on midi keyboard example
work on implementing removes for afuncs and cfuncs
fixed error with using :channels instead of :nchnls (was causing mono engines to be created always); restored add-events to take in normal events, and added add-engine-events as the convenience wrapper
cleanup