pharos 0.4.2

Observer pattern which generates a futures 0.3 stream of events
Documentation
# TODO

- use NonZeroUsize as parameter in bounded channel
- make Events clone? means we can only work with broadcast channels
- switch to more performant channels (crossbeam). 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?