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/Players/MacPlayer.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Threading.Tasks;
+using NetCoreAudio.Interfaces;
+
+namespace NetCoreAudio.Players
+{
+    internal class MacPlayer : UnixPlayerBase, IPlayer
+    {
+        protected override string GetBashCommand(string fileName)
+        {
+            return "afplay";
+        }
+
+        public override Task SetVolume(byte percent)
+        {
+            if (percent > 100)
+                throw new ArgumentOutOfRangeException(nameof(percent), "Percent can't exceed 100");
+
+            var tempProcess = StartBashProcess($"osascript -e \"set volume output volume {percent}\"");
+            tempProcess.WaitForExit();
+
+            return Task.CompletedTask;
+        }
+    }
+}