documentation: update my name (Ortmann -> Knüpfer)

boards/chronos/board_init.c

boards/chronos/drivers/battery.c

boards/chronos/drivers/buzzer.c

boards/chronos/drivers/display.c

boards/chronos/drivers/display_putchar.c

boards/native/board_config.c

boards/native/board_init.c

boards/native/drivers/native-led.c

boards/native/include/board.h

boards/native/include/board_internal.h

core/include/kernel_types.h

core/reboot.c

cpu/msp430-common/lpm_cpu.c

cpu/native/include/cpu.h

cpu/native/include/cpu_conf.h

cpu/native/include/native_internal.h

cpu/native/include/periph_conf.h

cpu/native/irq_cpu.c

cpu/native/lpm_cpu.c

cpu/native/native_cpu.c