Adds support to the library for tokio 0.2 backward-compatibility. This should hopefully benefit, and prevent lavalink-rs from being blocked on this feature.
These can be reached using, e.g., `gateway-tokio-02`, `driver-tokio-02`, `serenity-rustls-tokio-02`, and `serenity-native-tokio-02` features.
Naturally, this requires some jiggering about with features and the underlying CI, which has been taken care of. Twilight can't be handled in this way, as their last tokio 0.2 version uses the deprecated Discord Gateway v6.
This should make dropping `ChildContainer`s and their parent `Input`s safer in async contexts.
It seems like SIGINT is insufficient to make wait terminate, but SIGKILL suffices. This introduced a new problem, namely that we have to remember and wait on *every* pid we create. This should, hopefully, put the issue of zombie processes to bed for good.
Linux/Unix requires that processes be waited, which is unfortunate as Windows lets us abandon them to the murderous whims of the OS. This PR adds Unix-specific behaviour to send a SIGINT before waiting on the process, and adds an additional thread per call for asset disposal on all platforms.
Closes#38.
---
* Close processes by SIGINT and wait on Unix
This seems to remedy the Linux-specific zombie processes. Addition of
nix as a dependency *should* be fine on Windows, since I believe it
compiles to an empty crate.
* Dispose of Tracks on auxiliary thread
This adds a mechanism for the mixer threads to perform potentially expensive deallocation/cleanup outside of the main loop, preventing deadline misses etc. This should make misbehaving `wait`s a bit more friendly.
This implements a proof-of-concept for an improved audio frontend. The largest change is the introduction of events and event handling: both by time elapsed and by track events, such as ending or looping. Following on from this, the library now includes a basic, event-driven track queue system (which people seem to ask for unusually often). A new sample, `examples/13_voice_events`, demonstrates both the `TrackQueue` system and some basic events via the `~queue` and `~play_fade` commands.
Locks are removed from around the control of `Audio` objects, which should allow the backend to be moved to a more granular futures-based backend solution in a cleaner way.
