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

docs/input/cli/index.cshtml

@@ -0,0 +1,12 @@
+Title: CLI
+Order: 10
+---
+
+<h1>Sections</h1>
+
+<ul>
+@foreach (IDocument child in OutputPages.GetChildrenOf(Document))
+{
+  <li>@Html.DocumentLink(child)</li>
+}
+</ul>