Add C# TTS API (#399)

dotnet-examples/TTS/Struct/SherpaOnnxOfflineTtsModelConfig.cs

@@ -0,0 +1,23 @@
+using System.Runtime.InteropServices;
+
+namespace TTS.Struct
+{
+    [StructLayout(LayoutKind.Sequential)]
+    public struct SherpaOnnxOfflineTtsModelConfig
+    {
+        /// <summary>
+        /// 模型配置
+        /// </summary>
+        public SherpaOnnxOfflineTtsVitsModelConfig vits;
+        /// <summary>
+        /// 线程数
+        /// </summary>
+        public int num_threads;
+        public int debug;
+        /// <summary>
+        /// 使用cpu
+        /// </summary>
+        [MarshalAs(UnmanagedType.LPStr)]
+        public string provider;
+    }
+}