Merge pull request #789 from mannol1/master

Fixed several bugs and added some features
Fixed some possible ways connections could linger indefinitely without being killed.
Speeded up onion requests.

Also increased the maximum number of announce entries.
Fixed clients not connecting when there is only 2 people on the network.
send_custom_user_packet now returns -1 when friend is offline.
Reduced the number of useless onion packets sent.
Remove libtoxav.pc from git

libtoxav.pc is automatically generated by configure from libtoxav.pc.in
and should not be commited.
Merge pull request #792 from jin-eld/remove-libtoxav.pc

Remove libtoxav.pc from git
Added custom callback data and capability identifier