Add copyright header to all files

[lthibault]

• Determine what language should be included
• Determine strategy for efficiently inserting into existing code-base
• Git pre-commit hook to ensure all files have notice

[lthibault]

Circuit uses the following header:

// Copyright 2013 The Go Circuit Project
// Use of this source code is governed by the license for
// The Go Circuit Project, found in the LICENSE file.
//
// Authors:
//   2013 Petar Maymounkov <p@gocircuit.org>

[lthibault]

Docs for writing new pre-commit hooks.

This should be trivially-doable with a recursive grep that uses a regex to test for the header, and pattern-matches against the list of contributors.

[lthibault]

Clojure uses the following header:

/**
 *   Copyright (c) Rich Hickey. All rights reserved.
 *   The use and distribution terms for this software are covered by the
 *   Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
 *   which can be found in the file epl-v10.html at the root of this distribution.
 *   By using this software in any fashion, you are agreeing to be bound by
 * 	 the terms of this license.
 *   You must not remove this notice, or any other, from this software.
 **/