Merge pull request #502 from contiki-ng/release-4.1

.gitignore

.gitmodules

.travis.yml

LICENSE.md

Makefile.include

README.md

arch/cpu/arm/Makefile.arm

arch/cpu/arm/arm-def.h

arch/cpu/arm/arm.txt

arch/cpu/arm/common/SD-card/cfs-sdcard.c

arch/cpu/arm/common/dbg-io/dbg-printf.c

arch/cpu/arm/common/dbg-io/dbg-putchar.c

arch/cpu/arm/common/dbg-io/dbg-puts.c

arch/cpu/arm/common/dbg-io/dbg-snprintf.c

arch/cpu/arm/common/dbg-io/dbg-sprintf.c

arch/cpu/arm/common/dbg-io/strformat.c

arch/cpu/arm/common/dbg-io/strformat.h

arch/cpu/arm/common/sys/mtarch.c

arch/cpu/arm/common/sys/mtarch.h

arch/cpu/arm/common/usb/Makefile.usb