Fix: packet size and typo in transfer mode main -> mail

CI: split up Cortex-M4 in two groups

examples/default: remove trailing whitespaces

gitignore: ignore package directories

Fix UDP/ICMPv6 checksum for a sliced/accumulated payload.

drivers/at86rf2xx: don't inlcude the header in itselfs

net/gnrc/ipv6: de-inlined ipv6_addr_equal

drivers/pcd8544: fixed include guard

POSIX socket: source addr selection

Reworking timer in lm4f120, fix #4077

...and use it in POSIX sendto() function.

posix sockets: recvfrom on connectionless transports

A client should not require to explicitly call bind() to receive packets, but is expected to receive replies sent to the ephemeral port that was selected as a source port by the UDP implementation.

boards: fixed include guards

boards/limifrog-v1: fix uart configuration in periph_conf

Padding for an odd number of bytes was not calculated properly.

core/atomic.h: fix doxygen to get rid of warning

core: add support to see if there are messages available for the curr…

gnrc: networking minimal