Merge pull request #12 from JHSawatzki/master

Update for binding _delay_us to delayMicroseconds
Add comment to Makefile with links to other people's Makefiles
add avr/sleep.h for Teensy3, for Nordic BLE library
Add dummy EIMSK in avr_emulation, undo avr/sleep.h workaround
Add zero to USB serial number, workaround for Mac OS-X CDC-ACM bug
http://forum.pjrc.com/threads/25482-Duplicate-usb-modem-number-HELP!
HardwareSerial write functions need to be virtual
http://forum.pjrc.com/threads/25494-Problems-with-HardwareSerial-Pointer-and-write
Add crc16.h for AVR libc compatibility
Merge pull request #1 from PaulStoffregen/master

Merge