Added check to ensure that the available libsodium library is compatible

Tox now uses some crypto_pwhash functions that are only available in the
newer libsodium releases; check this in configure to prevent compile
time errors.
Fix link in TODO
Fixed build issue.
Merge branch 'patch-1' of https://github.com/her001/toxcore
Merge branch 'sodium-check' of https://github.com/jin-eld/ProjectTox-Core
Actually fixed build issue.
Audiobot v2