Merge pull request #3646 from authmillenon/posix/feat/sockets

Makefile.dep

examples/posix_sockets/Makefile

examples/posix_sockets/README.md

examples/posix_sockets/main.c

examples/posix_sockets/udp.c

sys/Makefile

sys/Makefile.include

sys/posix/include/arpa/inet.h

sys/posix/include/netinet/in.h

sys/posix/include/sys/bytes.h

sys/posix/include/sys/socket.h

sys/posix/pnet/netinet_in.c

sys/posix/pnet/sys_socket.c

sys/posix/sockets/Makefile

sys/posix/sockets/doc.txt

sys/posix/sockets/posix_sockets.c

tests/coap/Makefile