Give specs Platform flags
Add an IObserver implementation
IObservable<T> should never be null
Add an IObservable implementation that just returns a value
Always return a default Observable for any IO<T> type
Remove VS2013 Cruft
Gate everything to .NET 4.5
Adding acceptance test examples and modified code to pass

Created AutoObservableProvider to return sensible observables
  from sub members that return IObservable<T>. As the
  IObservable<T> type is an interface it would normally get a
  substitute automatically created for it. To override this
  behaviour, AutoObservableProvider must be before the
  AutoSubstituteProvider in the list of AutoValueProviders
  in SubstituteState.

Updated Task code to run on both NET4 and NET45 platforms.
Removing DefaultForType, relying on auto values instead