Removed the send withid functions

See also:
https://github.com/irungentoo/toxcore/commit/ff02d5a607362df1382eeb4d7ef146eaab1c8dd1
Some documentation, again
Added tox_add_tcp_relay

See also:
https://github.com/irungentoo/toxcore/commit/01203a22727ffb33bdeca702381e1d86e00bde2b