Add teensy3 i2clib#19

Merged

nseidle merged 2 commits intosparkfun:masterfrom

jogi-k:AddTeensy3_i2clib

Jan 11, 2021

Commits on Jan 8, 2021

Does not yet work
jogi-k
committed

Commits on Jan 9, 2021

Finally works, use #define to switch between Teensy >= 3.0 / LC and arduino
jogi-k
committed