Re-add default impl to SessionConfig and make Credentials::with_password generic over Into<String>
add docs for Credential
reintroduce old Default impl for SessionConfig
use the third argument for the track-to-play rather than a testing id
Previously, polling `AudioFileFetch` consisted of three parts: Handling
stream loader commands, handling received data, and triggering preloading
in stream mode when the number of open requests is sufficiently small. The
first steps use channels which are polled, and if something's available,
it's handled. The third step is executed on every call of `poll`.
The first two could easily be refactored using a `tokio::select!`-loop.
Therefore, counting the number of open requests was also refactored to fit
into this scheme. They were previously counted using a shared
`AtomicUsize`. Now, the number of open requests is stored exclusively in
`AudioFileFetch`, increased on starting a request, and decreased by an
oneshot channel that is fired when a request is finished.
This allows us to `select` that channel in the loop too, and since
loading ahead makes only sense if the number of open requests decreases,
the third step is only executed in this case.
`AudioFileFetch` does not implement `Future` anymore, but is rather used
as helper struct in an async fn `audio_file_fetch`.
* Use sub-crates of future
* Remove unnecessary pin-project
* Removed unused crates and features
* Replace futures channels by tokio channels
* Use serde's "derive" feature flag instead of serde_derive
* Remove default impl for `SessionConfig`
* Move util mod to single file
* Restore privacy of mods
* Move `fn get_credentials` to application
* Remove `extern crate` statements
Probably more simple than the previous approach which
doubles the code: Instead of implementing the `Open` trait,
we simply use custom SinkBuilder, one for the default host,
and one for the "jack" host.
