add support for Teensy LC, Teensy 3.5 and Teensy 3.6

[bmegli]

Use i2c_t3 library and I2C_NOSTOP for Teensy boards.

This commit extends #ifdef for Teensy 3.1/3.2 to all Teensy boards supported by i2c_t3.

For discussion on Teensy board detection see: https://forum.pjrc.com/threads/46694-Board-Specific-Compilation

[bmegli]

I am wondering if Teensy 3.0 should also be included.

It is supported by i2c_t3 so maybe the line should be:

//Teensy 3.0 (__MK20DX128__), Teensy 3.1/3.2 (__MK20DX256__), Teensy LC (__MKL26Z64__) Teensy 3.5 (__MK64FX512__), Teensy 3.6 (__MK66FX1M0__)
#if defined(CORE_TEENSY) && (defined(__MK20DX128__)  || defined(__MK20DX256__) || defined(__MKL26Z64__) || defined(__MK64FX512__) || defined(__MK66FX1M0__) )

The line is getting so long that some line-breaks seem necessary

[bmegli]

Reworked as:

/* For Teensy use i2c_t3 library and I2C_NOSTOP
   Teensy 3.0 (__MK20DX128__)
   Teensy 3.1/3.2 (__MK20DX256__)
   Teensy LC (__MKL26Z64__)
   Teensy 3.5 (__MK64FX512__)
   Teensy 3.6 (__MK66FX1M0__)
*/
#if defined(CORE_TEENSY)   && (  \
    defined(__MK20DX128__) ||    \
    defined(__MK20DX256__) ||    \
    defined(__MKL26Z64__)  ||    \
    defined(__MK64FX512__) ||    \
    defined(__MK66FX1M0__)    )