Add output abstraction and reorganize profile

* Moves ColorSystem from Profile to Capabilities
* Renames Tty to IsTerminal
* Adds IAnsiConsoleOutput to make output more flexible

Closes #343
Closes #359
Closes #369

src/Spectre.Console/AnsiConsoleOutput.cs

@@ -0,0 +1,58 @@
+using System;
+using System.IO;
+using System.Text;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Represents console output.
+    /// </summary>
+    public sealed class AnsiConsoleOutput : IAnsiConsoleOutput
+    {
+        /// <inheritdoc/>
+        public TextWriter Writer { get; }
+
+        /// <inheritdoc/>
+        public bool IsTerminal
+        {
+            get
+            {
+                if (Writer.IsStandardOut())
+                {
+                    return !System.Console.IsOutputRedirected;
+                }
+
+                if (Writer.IsStandardError())
+                {
+                    return !System.Console.IsErrorRedirected;
+                }
+
+                return false;
+            }
+        }
+
+        /// <inheritdoc/>
+        public int Width => ConsoleHelper.GetSafeWidth(Constants.DefaultTerminalWidth);
+
+        /// <inheritdoc/>
+        public int Height => ConsoleHelper.GetSafeHeight(Constants.DefaultTerminalWidth);
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="AnsiConsoleOutput"/> class.
+        /// </summary>
+        /// <param name="writer">The output writer.</param>
+        public AnsiConsoleOutput(TextWriter writer)
+        {
+            Writer = writer ?? throw new ArgumentNullException(nameof(writer));
+        }
+
+        /// <inheritdoc/>
+        public void SetEncoding(Encoding encoding)
+        {
+            if (Writer.IsStandardOut() || Writer.IsStandardError())
+            {
+                System.Console.OutputEncoding = encoding;
+            }
+        }
+    }
+}