Ship ReactiveUI 6.0

ReactiveUI 6.x is now in Ship It Mode, the :squirrel: must be given its Due.

## [DO THIS BEFORE SHIPPING](https://github.com/reactiveui/ReactiveUI/milestones/ReactiveUI%206.0)

- [x] Consider rewriting ReactiveCommand still. 
- [x] Need to make Android Support into a separate lib, it conflicts too much with other stuff (/cc @onovotny) (#571)
- [x] Suspend / Resume is mostly weird and broken on multiple platforms (#570)
- [x] Whatever gets announced at BUILD, we're this close already, may as well (#552)
- [ ] Wait for Rx.NET to include Profile259. (#569)

## What has Shipped:

* Fix up collection interfaces (#432)
* Xamarin moves to PCLs (#438)
* ReactiveUI is now based on Splat (#451)
* Nuke legacy ReactiveCommands (ty @jlaanstra)
* Remove IO<T> as an interface from OAPH (ty @niik)
* Move service location + logging + unit test detection to Splat, make ReactiveUI depend on it, so that Akavache doesn't need ReactiveUI and everyone can share service location / logging without buying into RxUI
* Ship 6.0 Alpha
* Attach CanExecute to Bound Commands on iOS (#469)
* Add ReactiveListAdapter, Android binding improvements (#470)
* ViewPager adapter (#494)
* Add Blend for Windows 8.1 (#487) 
* Remove scheduling (#516)
* Rewritten ReactiveCommand (#521)
* Activation framework (#503, #526)
* Asynchronous intent results on Android (#528) 
* Reactive subclasses for many more Cocoa objects 
* Event leak fixes on XAML-based platforms (#547, #549)
* Generic Cocoa classes for collection and table view sources (#448)
* Make sure people who naively await events don't deadlock (#586)
* Move ReactiveUI to a single DLL (#587)
* Cocoa scheduler now runs items sequentially on the UI thread (#600)
* WinForms view caching (#603)

## Breaking Changes

- **Anything dependending on the non-generic `IReactiveCollection`**. I believe you can just use the generic variant almost everywhere, since every collection type in ReactiveUI is generic.
- **Anything implementing `IReactiveCollection<T>` only loses the type `IReactiveCollection`**. All its interfaces are still implemented by the generic variant.
- **The `IReactiveCollection<T>` interface no longer implements `ICollection<T>`**. However it does still implement `IEnumerable<T>`.
* ReactiveUI now depends on the Microsoft version of Rx, version 2.2.2
* `IEnableLogger` now needs a `using Splat;`
* `InitializeResolver` => `InitializeSplat` + `InitializeReactiveUI`
* Legacy ReactiveUI 4.x commands are gone - pull them from source if you need them
* ObservableAsPropertyHelper is now no longer directly IObservable. Use `WhenAny` to get to these properties instead of grabbing the backing field.
* MemoizingMRUCache and ObservableAsyncMRUCache are both removed - the former has moved to Splat (add a `using Splat;` to fix this), and the latter is deprecated. Akavache is a better solution for ObservableAsyncMRUCache.
* ReactiveUI now no longer implicitly schedules things to the UI thread for you except for `RegisterAsync`. If you were relying on this, you probably need to add some `ObserveOn(RxApp.MainThreadScheduler)`s
* ReactiveCommand is a lot different. See #521 for more.
* ReactiveUI on iOS now requires Xamarin.iOS 7.2.1 or higher
* No more references to ReactiveUI.Platforms - NuGet should handle this Automagically

## Find And Replace Breaking Changes

* `RxApp.DependencyResolver` => `Locator.Current`
* `RxApp.MutableResolver` => `Locator.CurrentMutable`
* `RxApp.InUnitTestRunner` => `ModeDetector.InUnitTestRunner`