Move Wasmtime for .NET to the Wasmtime repo.

This moves the Wasmtime for .NET implementation to the Wasmtime repo.

Wasmtime for .NET is a binding of the Wasmtime API for use in .NET.

crates/misc/dotnet/examples/memory/Program.cs

@@ -0,0 +1,31 @@
+using System;
+using Wasmtime;
+
+namespace HelloExample
+{
+    class Host : IHost
+    {
+        public Instance Instance { get; set; }
+
+        [Import("log")]
+        public void Log(int address, int length)
+        {
+            var message = Instance.Externs.Memories[0].ReadString(address, length);
+            Console.WriteLine($"Message from WebAssembly: {message}");
+        }
+    }
+
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            using (var engine = new Engine())
+            using (var store = engine.CreateStore())
+            using (var module = store.CreateModule("memory.wasm"))
+            using (dynamic instance = module.Instantiate(new Host()))
+            {
+                instance.run();
+            }
+        }
+    }
+}