pyterm: enable TCP connection to remote host
net_if: alternative approach for swapping the byte order
Merge pull request #1948 from OlegHahm/netif_byteorder

Netif fix byteorder
auto_init: always set source address mode
Merge pull request #1957 from OlegHahm/auto_init_addr_mode

auto_init: always set source address mode
pyterm: make mostly pep8 compliant
drivers/periph/rtt: added overflow callback
Merge pull request #1950 from OlegHahm/pyterm_tcp_remote

pyterm: enable TCP connection to remote host
cpu/nrf51822: adjusted to RTT interface changes
cpu/stm32f1: adjusted to RTT interface changes
core: put more intelligence into `queue_msg()`

Fixes #1942.

There were two instances were it was not checked the target thread has a
message queue before queuing the message.

This PR centralizes the check into `queue_msg()`.
Merge pull request #1960 from haukepetersen/enh_driver_rtt

drivers: added enhanced RTT driver interface
Merge pull request #1961 from Kijewski/issue-1942

core: put more intelligence into `queue_msg()`
c++: sys: add extern C to header files
[SQUASH ME] addressed comments
[SQUASH ME] removed unrelated newlines/whitespaces
[SQUASH ME] moved the `extern "C"` out of the `#if` block and readded the whitespaces
[SQUASH ME] added missing `extern "C"`s