Merge branch 'zero' of github.com:arduino/ArduinoZero into zero_servo

bootloaders/zero/Debug/Exe/samd21_sam_ba.bin

bootloaders/zero/Debug/Exe/samd21_sam_ba.out

bootloaders/zero/Debug/List/samd21_sam_ba.map

bootloaders/zero/Makefile

bootloaders/zero/Release/Exe/samd21_sam_ba.bin

bootloaders/zero/Release/Exe/samd21_sam_ba.out

bootloaders/zero/Release/List/samd21_sam_ba.map

bootloaders/zero/drivers/cdc_enumerate.c

bootloaders/zero/drivers/cdc_enumerate.h

bootloaders/zero/drivers/uart_driver.h

bootloaders/zero/main.c

bootloaders/zero/main.h

bootloaders/zero/sam_ba_monitor.c

bootloaders/zero/samd21_sam_ba.bin

bootloaders/zero/samd21_sam_ba.ewp

bootloaders/zero/samd21_sam_ba.eww

bootloaders/zero/samd21j18a_flash.ld

bootloaders/zero/startup_samd21.c

bootloaders/zero/usart_sam_ba.c

bootloaders/zero/utils/compiler.h