TODO

instead of providing channels, just take a Sink in observe? That would keep the lib much simpler and allow users more flexibility.
ObserveOnce = observable without events being clone? Handy for types that want to provide a detached stream over types that don't implement clone or for arbitrary user types. Came up during the dev of async_nursery.
be abstract over channels like thespis?
try_recv, which allows just checking if there is an event without blocking the task until there is, handy for cooperative cancellation.
use matches! in docs and examples for filters.
test on wasm
should Pharos be Sync?
use NonZeroUsize as parameter in bounded channel
make Events clone, means we can only work with broadcast channels
switch to more performant channels (flume?). Will be easier once they provide an async api.
allow other channel types, like a ringchannel which drops messages on outpacing? To prevent DDOS and OOM attacks?

Rewrite goals:

Events to be clone so something that is observing can clone it's stream and give it to some other object/task. Or make Events Observable itself?
be channel agnostic?

Sending out to observers is async and provides back pressure. Other sends and adding observers requires that we are not in the middle of sending out.