Upgraded to latest Rust-Empty
Upgrade to latest Rust
Fix lifetimes for AudioSpec.

We seem to nee the extra `'call` lifetime parameter on AudioSpec::load_wav_rw because
rustc seems to infer `'a` otherwise.
Fix Drop trait on generic struct Timer

Recent rust versions forbid Drop on generic traits.
Implement drop in an embedded non-generic struct instead.

Additionally, since the SDL timer runs on a separate thread, use
an AtomicInt for the timer_id to ensure that we only remove a timer
once.