File sending.
Basic ntox file sending.
File sending now works on bad wireless connections.
Core now takes better care of file transfers.
nTox updated with changes in core, some file sending things fixes.
Removed useless ifdefs.
Fixed bug.
Max length of filenames is now 255 bytes.
File control packets can now be used by the person sending the file.
Merge branch 'file-transfers' of https://github.com/irungentoo/ProjectTox-Core into file-transfers
File sending added to public api.
Merge branch 'file-transfers'

File transfers are now working and in public api.