Teensy 3.6 Compatibility

[embedded-creations]

Some issues captured in this thread: https://community.pixelmatix.com/t/teensy-3-5-with-vers-3-sm-board-and-aurora/288/13

[marcmerlin]

there are fixes in the teensy3.6 branch
8df7706
and
7b78ce3
which I also integrated in
marcmerlin/FastLED_NeoMatrix_SmartMatrix_LEDMatrix_GFX_Demos@461145c