Make core Ticker abstract and public (#116)

* Make core Ticker abstract and public
Make the core Ticker abstract and public so it can be inherited by platform
implementations; remove now-unused parts of original Ticker; add CreateTicker
to IPlatformServices; remove unused CreateTimer methods from IPlatformServices

* Add docs for Ticker

* Remove unnecessary Ticker.Default set

* Move Ticker into Internals

* Update Ticker docs

* Remove old Ticker docs

* Remove commented code

1 files changed, 2 insertions, 6 deletions

diff --git a/Xamarin.Forms.Core/IPlatformServices.cs b/Xamarin.Forms.Core/IPlatformServices.cs
index e4a3ce0b..a01baa02 100644
--- a/Xamarin.Forms.Core/IPlatformServices.cs
+++ b/Xamarin.Forms.Core/IPlatformServices.cs
@@ -3,6 +3,7 @@ using System.IO;
 using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
+using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms
 {
@@ -12,12 +13,7 @@ namespace Xamarin.Forms
 
 		void BeginInvokeOnMainThread(Action action);
 
-		//this will go once Timer is included in Pcl profiles
-		ITimer CreateTimer(Action<object> callback);
-		ITimer CreateTimer(Action<object> callback, object state, int dueTime, int period);
-		ITimer CreateTimer(Action<object> callback, object state, long dueTime, long period);
-		ITimer CreateTimer(Action<object> callback, object state, TimeSpan dueTime, TimeSpan period);
-		ITimer CreateTimer(Action<object> callback, object state, uint dueTime, uint period);
+		Ticker CreateTicker();
 
 		Assembly[] GetAssemblies();