Merge pull request #1701 from thomaseichinger/samr21

boards/samr21-xpro/Makefile

boards/samr21-xpro/Makefile.include

boards/samr21-xpro/board.c

boards/samr21-xpro/dist/debug.sh

boards/samr21-xpro/dist/flash.sh

boards/samr21-xpro/include/board.h

boards/samr21-xpro/include/periph_conf.h

cpu/cortex-m0_common/include/core_cm0plus.h

cpu/samd21/Makefile

cpu/samd21/Makefile.include

cpu/samd21/cpu.c

cpu/samd21/hwtimer_arch.c

cpu/samd21/include/component/component_ac.h

cpu/samd21/include/component/component_adc.h

cpu/samd21/include/component/component_dac.h

cpu/samd21/include/component/component_dmac.h

cpu/samd21/include/component/component_dsu.h

cpu/samd21/include/component/component_eic.h

cpu/samd21/include/component/component_evsys.h

cpu/samd21/include/component/component_gclk.h