Introduce WhenAnyValue() mixin

As suggested in #342, simplifies the 99% case of only caring about the
changed value.
Add Microsoft.Reactive.Testing built from mono/rx
Fix up the old and busted RxUI.Testing_Mono csproj file
What is happening
Merge pull request #344 from reactiveui/rxui-testing-monomac

RxUI.Testing for MonoMac
ReactiveCommand can set initial CanExecute state

ReactiveCommand's constructor can optionally set the initial CanExecute
state.  Originally, it defaulted to true, until your canExecute observer
told it otherwise.  It is of course possible to forced the state to
false before binding it to anything, but this removes that nescessity
Create some global constants for cache limits
Set the cache limits on a bunch of internal caches
Add an android manifest whatever just stop doing this constantly
Merge pull request #345 from sillyotter/reactive-command-initial-condition

ReactiveCommand can set initial CanExecute state
Use the correct constant for Xamarin.iOS
Merge pull request #346 from reactiveui/less-caching

Use less caching on mobile platforms
Don't instantiate all the items in the resolver if we only want the last one
Moved filter on _suppressionRefCount to subscription declarations in setupRX() to allow cleaner overrides of the raiseXXXX methods
Winforms command binding + tests
Optimized versions of the AddRange and InsertRange methods. Making use of List<T> AddRange and InsertRange methods
Optimized RemoveRange method to use the inner List<T> RemoveRange method
Added ReactiveBindingList implementation + tests to support winforms databinding
Added some default property bindings + tests
Add ViewModelWhenAnyValueDynamic to save a call to Reflection.ExpressionToPropertyNames.

Make this.OneWayBind(x => x, ...) bindings work, fixes #331.

Remove unused directive for Silverlight.