F# API modifications + more examples

I've created some new F# API modifications:

- Extended default F# Actor interface with Context property (to access ActorContext) and spawn extension method (to enable use `spawn`-like creation of child actors)
- Modified previous SupervisorStrategy-aware function parameters according to the @thinkbeforecoding comments.
- Added `Strategy` module with functions allowing creation of OneForOne and AllForOne supervisor strategies in way enhancing F# syntax (function currying, using F# lambdas).

Additionally I've created an examples (Supervisioning.fs) to show possible usage of new API functions. Furthermore I've attached example of MapReduce algorithm using F# functional API (as I've described on my blog in details - http://bartoszsypytkowski.com/blog/2014/07/09/fsharp-akka-map-reduce/).