Scala Adaptor Improvements

Includes groupBy, scala README, examples, moving ImplicitFunctionConversions out of internal package, multicast, publish, replay, and methods for BlockingObservable.

Note that the commit https://github.com/samuelgruetter/RxJava/commit/ac26e42d1e85deac0b7bfa50c3ca3e5298493dd4 modifies core by making the Java `Subject<T, R>` used as contravariant in `T` and covariant in `R`, which allows me to write Scala's multicast without typecasting.