Add Spectre.Cli to Spectre.Console

* Renames Spectre.Cli to Spectre.Console.Cli.
* Now uses Verify with Spectre.Console.Cli tests.
* Removes some duplicate definitions.

Closes #168

examples/Cli/Injection/Program.cs

@@ -0,0 +1,23 @@
+using Injection.Commands;
+using Microsoft.Extensions.DependencyInjection;
+using Spectre.Console.Cli;
+
+namespace Injection
+{
+    public class Program
+    {
+        public static int Main(string[] args)
+        {
+            // Create a type registrar and register any dependencies.
+            // A type registrar is an adapter for a DI framework.
+            var registrations = new ServiceCollection();
+            registrations.AddSingleton<IGreeter, HelloWorldGreeter>();
+            var registrar = new TypeRegistrar(registrations);
+
+            // Create a new command app with the registrar
+            // and run it with the provided arguments.
+            var app = new CommandApp<DefaultCommand>(registrar);
+            return app.Run(args);
+        }
+    }
+}