Herald v2 (#74)

* Add speech rate setting

* Add volume slider

* New speech manager skeleton

* User API key from resx

* Implement voice list retrieve via new api

* Rewrite to use ObAPI, remove all dependancies

* Use volume setting

* Clean up using statements

* Volume and timing adjustments

* Lookup rate value

* Use numeric rates for tighter spread

* Manage plugin data folder via core interface

* Add check that nullable settings are not null.

* Get file size before it's deleted.

* Improve old settings migration.

* Ignore cache sizes below 1MB

* Re-index orphaned files in cache, purge legacy wav files.

* Call top level error logging for native voice exception.

* Async title and detail requests to remove pause

* Remove NetCoreAudio use of temp files.

* Remove orphan using.

ObservatoryHerald/NetCoreAudio/Interfaces/IPlayer.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Threading.Tasks;
+
+namespace NetCoreAudio.Interfaces
+{
+    public interface IPlayer : IDisposable
+    {
+        event EventHandler PlaybackFinished;
+
+        bool Playing { get; }
+        bool Paused { get; }
+
+        Task Play(string fileName);
+        Task Pause();
+        Task Resume();
+        Task Stop();
+        Task SetVolume(byte percent);
+    }
+}