Teensyduino 1.31

Add support for Arduino 1.6.12
Arduino SD library support 4 bit SDIO on Teensy 3.5 & 3.6 (special thanks WMXZ)
Fix EEPROM on Teensy 3.6 with CPU speed > 120 MHz (special thanks Defragster)
Update FlexCAN library for CAN1 on Teensy 3.6 (Pawelsky)
Update OctoWS2811 to support Teensy 3.5 & 3.6
Fix USB serial number on Teensy 3.6 with CPU speed > 120 MHz
Fix audio I2S output on Teensy 3.6 with CPU speed > 120 MHz when also using I2S input
Support Teensy 3.5 & 3.6 on older versons of Arduino
Fix SPI1 default SCK1 pin (KurtE)
Optimize attachInterrupt (tni)
Improve USB stability on Teensy 3.6 with CPU 180 or 216 MHz
Add USB MIDI custom name example
Fix Adafruit_ST7735 on Teensy 3.5 & 3.6 (MichaelMeissner)
Many library metadata files updated for PlatformIO
Fix Ethernet library socket receive bug (thanks ElOtroMateo)
Fix compiler warnings, eg: kinetis_hsrun_enable unused
Serial buffer sizes override from command line (Frank B)
Stream find functions use const for pointers
Add AudioOutputAnalogStereo and AudioInputAnalogStereo
Add Audio reverb effect (Joao Rossi Filho)
Add Audio waterfall spectrum example (Nathaniel Quillin)
Fix USB Audio on Windows when used with USB Serial
Fix auto-reboot for newer USB types
Fix serial monitor for newer non-serial USB types
Many ILI9341_t3 improvements (Frank B, Kurt E, Softegg)
SerialFlash allows other SPI ports (Martino Facchin)
Teensy Loader shows correct images for Teensy 3.5 & 3.6
Improved handling of float INF & NAN (Frank B)
Bundle libpng12 & libusb10 libraries, missing from some Linux distros.