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/Commands/DefaultCommand.cs

@@ -0,0 +1,30 @@
+using System;
+using System.ComponentModel;
+using Spectre.Console.Cli;
+
+namespace Injection.Commands
+{
+    public sealed class DefaultCommand : Command<DefaultCommand.Settings>
+    {
+        private readonly IGreeter _greeter;
+
+        public sealed class Settings : CommandSettings
+        {
+            [CommandOption("-n|--name <NAME>")]
+            [Description("The person or thing to greet.")]
+            [DefaultValue("World")]
+            public string Name { get; set; }
+        }
+
+        public DefaultCommand(IGreeter greeter)
+        {
+            _greeter = greeter ?? throw new ArgumentNullException(nameof(greeter));
+        }
+
+        public override int Execute(CommandContext context, Settings settings)
+        {
+            _greeter.Greet(settings.Name);
+            return 0;
+        }
+    }
+}