support for Teensy 3.x via Teensy.mk
minor tweaks to Teensy.mk
Teensy.mk: default to arm-none-eabi-xxx for executable names. Tweak the upload/reset stuff a little more. Add COPYRIGHT block.
Added Teensy to HISTORY.md
Added BlinkTeensy example which uses the Teensy.mk file.
Make BlinkTeensy a NON_TESTABLE_EXAMPLES
move ARDUINO_DIR auto-detection into Common.mk. This allows Teensy.mk to use auto-detected location.
Teensy.mk: simplify setting of MCU and MCU_FLAG_NAME
put ARDUINO_DIR block after Travis-CI block else travis will fail.
added info about Teensy to README.md
Merge pull request #281 from stepcut/teensy.mk

Add support for Teensyduino 3.x
Merge pull request #282 from sej7278/master

Add "avrispmkii" to the list of ISP's that don't have a port.

Fix #279