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/IGreeter.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace Injection
+{
+    public interface IGreeter
+    {
+        void Greet(string name);
+    }
+
+    public sealed class HelloWorldGreeter : IGreeter
+    {
+        public void Greet(string name)
+        {
+            Console.WriteLine($"Hello {name}!");
+        }
+    }
+}