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/Demo/Verbosity.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Globalization;
+
+namespace Demo
+{
+    public enum Verbosity
+    {
+        Quiet,
+        Minimal,
+        Normal,
+        Detailed,
+        Diagnostic
+    }
+
+    public sealed class VerbosityConverter : TypeConverter
+    {
+        private readonly Dictionary<string, Verbosity> _lookup;
+
+        public VerbosityConverter()
+        {
+            _lookup = new Dictionary<string, Verbosity>(StringComparer.OrdinalIgnoreCase)
+            {
+                { "q", Verbosity.Quiet },
+                { "quiet", Verbosity.Quiet },
+                { "m", Verbosity.Minimal },
+                { "minimal", Verbosity.Minimal },
+                { "n", Verbosity.Normal },
+                { "normal", Verbosity.Normal },
+                { "d", Verbosity.Detailed },
+                { "detailed", Verbosity.Detailed },
+                { "diag", Verbosity.Diagnostic },
+                { "diagnostic", Verbosity.Diagnostic }
+            };
+        }
+
+        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        {
+            if (value is string stringValue)
+            {
+                var result = _lookup.TryGetValue(stringValue, out var verbosity);
+                if (!result)
+                {
+                    const string format = "The value '{0}' is not a valid verbosity.";
+                    var message = string.Format(CultureInfo.InvariantCulture, format, value);
+                    throw new InvalidOperationException(message);
+                }
+                return verbosity;
+            }
+            throw new NotSupportedException("Can't convert value to verbosity.");
+        }
+    }
+}