OMEGA REFACTOR! Perf grind basically complete.

Resolves #70, Resolves #67

Still needs some regression testing in general, and a definite
regression is that rotary encoders are no longer (for the immediate time
being) supported.

Moves to a much simpler internal state tracking system, and FAR lighter
matrix scan.

Removes MicroPython support entirely.

kmk/mcus/circuitpython_samd51.py

@@ -0,0 +1,6 @@
+from kmk.firmware import Firmware as _Firmware
+from kmk.hid import CircuitPythonUSB_HID
+
+
+class Firmware(_Firmware):
+    hid_helper = CircuitPythonUSB_HID