Lay groundwork for new Spotify API before removing `spirc`
* Add token provider
* Introduce HTTP client
* Introduce caching `ApResolver` component
* Remove `keymaster` and update example
* Use `PacketType` instead of hex identifiers
* Document new unknown packet 0xb6
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.
Tests currently fail with some apt error:
> E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
This change would add the suggested `apt-get update`
it is pointless to run CI jobs for pushes / PRs that only change files that
would never cause a failure, such as documentation.
this avoids wasting resources for such situations.
