Long datarefs for USB flight sim controls

Added full support for Midi Time Codes and Real Time messages

can now receive and send Midi Time Codes
and send Real Time messages

https://forum.pjrc.com/threads/28932-LC-is-10-9-times-slower-than-T3-1?p=76072&viewfull=1#post76072

Fix packet stuffing in usb_flightsim_flush_callback

https://forum.pjrc.com/threads/25153-PDB0CH1-register-definitions

https://forum.pjrc.com/threads/28932-LC-is-10-9-times-slower-than-T3-1?p=75775&viewfull=1#post75775

https://forum.pjrc.com/threads/28932-LC-is-10-9-times-slower-than-T3-1

LC TPM DMA Enable bit

https://forum.pjrc.com/threads/28325-Teensy-LC-and-delay

strlen is already in string.h

or, alternativly one could write size_t strlen(const char *s) {return __builtin_strlen(s);} to use the gcc-builtin function.
I think, both are faster than the bytewise search.

millis()

systick_millis_count is already volatile, doing it twice is not needed.

Update kinetis.h

- Added bit definitions for the PIT
- limited Teensy LC to only two PITs
- added PIT_LTMR64 for Teensy LC

Update README.md

CS initialization corrected

Add some missing NVIC definitions