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
Merge pull request #795 from mannol1/master

Added custom callback data and capability identifier
Changed msi callbacks
Merge pull request #796 from mannol1/master

Changed msi callbacks
Removed logging to stderr and fixed timeout handling
Invoke callback via invoke_callback func
Merge pull request #798 from mannol1/master

Fixed segfault, timeout handling and logging.
Detailed docs for TCP server pretty much done.

Implementation coming soon.