-Fixed memory leak in datasave().
-Made some types more clean, such as using size_t instead of uint32_t and size_t instead of int.
-Removed unneccessary length checks
The following has been done:
* rename tox_{get,set} to tox_self_{get,set}
* rename tox_{get,set}_friend to tox_friend_{get,set}
* use *_size() functions instead of a return status
* pass NULL to discard error handler in _friend_ functions
