[SQUASH ME] test: add toolchain download and verbose output to travis
tests: blacklist examples that fail due to missing header files
boards: arduino-mega2560: cleanup of Makefiles
boards: arduino-mega2560: cleanup of periph_conf.h: remove left overs from
other board
boards: arduino-mega2560: fix indentation in errno.h
boards: arduino-mega2560: fix LED related defines
boards: arduino-mega2560: clean up LED init
cpu: atmega_common: move irq macros to irq_arch.c, fix indentation and doxgen
cpu: atmega2560: clean up Makefile
cpu: atmega2560: fix comment style
cpu: atmega2560: fix whitespace errors in header files and Makefile (periph)
cpu: atmega2560: move uart-related ISR to periph/uart.c, cleanup and comment
about custom vector table
cpu: atmega2560: fix newlines, whitespaces and typos in periph/timer.c