A/V integration in progress.

Added functions to send/receive msi packets via secure messenger
connections.

Made function to get the ip/port of a friend in Messenger.c public
Toxmsi build fix

Build failed on toxmsi building with
../toxmsi/AV_codec.c:46:28: fatal error: toxrtp_message.h: No such file or directory
 #include "toxrtp_message.h"
Merge pull request #619 from rayslava/master

Toxmsi build fix
Update TODO
Added resume support if the connection breaks during file sending.
Updated public api.
Merge pull request #621 from kigu/patch-3

Update TODO
Do not build tox_sync on win32
Merge pull request #622 from jin-eld/no-tox-sync-on-windows

Do not build tox_sync on win32
Added some things to the TODO list.
Fixed building on windows.