Move terminal example from //sky/examples to //examples

sky/examples/terminal/terminal_display.dart

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-import 'dart:async';
-
-// Interface for a terminal display, able to accept bytes (from the computer)
-// and typically displaying them (or possibly handling them as escape codes,
-// etc.) and able to get bytes from the "user".
-abstract class TerminalDisplay {
-  void putChar(int byte);
-  Future<int> getChar();
-
-  // TODO(vtl): Should probably also have facilities for putting many bytes at a
-  // time or getting as many bytes as available.
-}