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/Internal/Parsing/CommandTree.cs

@@ -0,0 +1,37 @@
+using System.Collections.Generic;
+
+namespace Spectre.Console.Cli.Internal
+{
+    internal sealed class CommandTree
+    {
+        public CommandInfo Command { get; }
+        public List<MappedCommandParameter> Mapped { get; }
+        public List<CommandParameter> Unmapped { get; }
+        public CommandTree? Parent { get; }
+        public CommandTree? Next { get; set; }
+        public bool ShowHelp { get; set; }
+
+        public CommandTree(CommandTree? parent, CommandInfo command)
+        {
+            Parent = parent;
+            Command = command;
+            Mapped = new List<MappedCommandParameter>();
+            Unmapped = new List<CommandParameter>();
+        }
+
+        public ICommand CreateCommand(ITypeResolver resolver)
+        {
+            if (Command.Delegate != null)
+            {
+                return new DelegateCommand(Command.Delegate);
+            }
+
+            if (resolver.Resolve(Command.CommandType) is ICommand command)
+            {
+                return command;
+            }
+
+            throw CommandParseException.CouldNotCreateCommand(Command.CommandType);
+        }
+    }
+}