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

src/Spectre.Console/Cli/IRemainingArguments.cs

@@ -0,0 +1,21 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Spectre.Console.Cli
+{
+    /// <summary>
+    /// Represents the remaining arguments.
+    /// </summary>
+    public interface IRemainingArguments
+    {
+        /// <summary>
+        /// Gets the parsed remaining arguments.
+        /// </summary>
+        ILookup<string, string?> Parsed { get; }
+
+        /// <summary>
+        /// Gets the raw, non-parsed remaining arguments.
+        /// </summary>
+        IReadOnlyList<string> Raw { get; }
+    }
+}