Fix test_many_clients in tox_test

Stack variable to_comp goes out of scope,
but a reference to the variable is used later
in Fiend_Requests.
Merge branch 'master' of https://github.com/pyruvate/toxcore
Added function to get public and private key from Tox object.
Updated download page link.
Fixed possible threading issues.

send_lossy_cryptpacket() can get called from another thread meaning
the connection can be killed while the packet is sending.
Adding a new connection while a lossy packet is being sent could
also cause thread related issues.
2 channel audio