teensy-core-4.1

Teensy 4.1 core updated for C++20

Historia

John Robinson 20c3d93b92 move source under core/ directory - adds a "namespace" for each header - makes clear where a header is expected to come from - better facilitates explicit includes		4 lat temu
..
atomic.h	move source under core/ directory	4 lat temu
crc16.h	move source under core/ directory	4 lat temu
delay.h	move source under core/ directory	4 lat temu
parity.h	move source under core/ directory	4 lat temu