Eventloop Implementation for Android/iOS/Xaml/Mac/WinRT

See: https://github.com/paulcbetts/splat/issues/77

First run at an implementation. I haven't edited the project files yet, but I can do so once the code is reviewed. The Android/iOS/Xaml implementation have all been tested. The WinRT code appears to compile but I don't have access to the platform to test. The Mac code is nearly identical to iOS but I don't have a license to test it with.


http://msdn.microsoft.com/en-us/library/bb386039.aspx 

"A IDisposable.Dispose method should not throw an exception. Dispose is often called as part of the clean up logic in a finally clause. Therefore, explicitly throwing an exception from Dispose forces the user to add exception handling inside the finally clause."