define some milestones

[ilya-epifanov]

I propose the following:

1. code coverage >90% (right now it's only ~50%), it's easy to get 100% here (Tee is actually 99% covered, remaining 1% seems to be due to a bug in emma)
2. good examples besides tests, examples showing different sources and sinks with the same machine should be especially impressive (i.e. listening for messages as an akka actor, reading them directly from a file or reading an in-memory list)
3. [future] Wye deserves some love (it could have same joins as Tee has now)