* Fix `toxav_get_tox` to return tox, not messenger.
* Fix the casts from Tox* to Messenger* in toxav_old.c.
* Pass Tox instead of Messenger to public group AV callbacks.
* No anonymous structs.
* No assignment expressions.
* Only one declarator per struct member declaration.
* Named callback types only, no inline types.
* No `;` empty statements.
* `++i` instead of `i++`.
Avoiding a cast in toxav_old.c avoids some potential (and real) bugs.
"All rights reserved" was incorrect. The project was licensed under GPL3,
which means a lot of rights are licensed to everybody in the world, i.e.
not reserved to the "Tox Project".
