* 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.
* Moved PAIR to toxav, where it's used (but really this should die).
* Replace most MIN calls with typed `min_*` calls. Didn't replace the
ones where the desired semantics are unclear. Moved the MIN macro to
the one place where it's still used.
* Avoid assignments in `while` loops. Instead, factored out the loop body
into a separate `bool`-returning function.
* Use named types for callbacks (`_cb` types).
* Avoid assignments in `if` conditions.
* Removed `MAKE_REALLOC` and expanded its two calls. We can't have
templates in C, and this fake templating is ugly and hard to analyse
and debug (it expands on a single line).
* Moved epoll system include to the .c file, out of the .h file.
* Avoid assignments in expressions (`a = b = c;`).
* Avoid multiple declarators per struct member declaration.
* Fix naming inconsistencies.
* Replace `net_to_host` macro with function.
This change does not include the addition of VP9. We do that in a
separate pull request.
Changes:
* fix the video bug (video frames larger than 65KBytes) by sending full
frame length in alternate header field
* improve video frame reconstruction logic with slots
* configure video encoder and decoder to be multihtreaded
* set error resilience flags on video codec
* change encoder and decoder softdeadline
