Akka.Persistence - F# guaranteed delivery, more tests, moved projects

[Horusiath]

• Akka.Persistence.FSharp and PersistenceExample.FsApi has been moved to src/core and src/examples directories (they were directly in src/ before).
• Changes considering F# persistence plugin API:
  • exec method doesn't affect the aggregate state now - it can be modified from that method by emitting events with callback in Persist, AsyncPersist and Defer methods of the eventsourced parameter.
  • Methods mentioned above has switched params (callback is defined first, sequence of events second) - I think it better reflects a F#-way of dealing with sequential data
• F# persistence plugin now exposes a function to spawning guaranteed delivery actors.
• PersistentViewSpec.PersistentView_should_run_size_limited_updates_on_user_request test has been fixed.

[rogeralsing]

@Horusiath can you fix this PR?
Looks good but can't be merged atm

[Horusiath]

I've fixed some of the compilation problems with F# projects and applied some of the @dsyme suggestions from #538 review:

• Changed Akka.FSharp from module to namespace, rest of the exposed API has been splitted into separate AutoOpen modules.
• Strategy factory functions have been refactored to static methods with optional arguments.
• pub, sub and unsub changed to publish, subscribe and unsubscribe

All of the changes has been updated in docs and examples.