Added license info.

COPYING

@@ -0,0 +1,37 @@
+The source files in the ./source directory, the build script ./build.d, and all of the graphics in ./bin/gfx are freely available in the public domain. Please do whatever you want with them.
+
+===============
+The files in the ./import/derelict directory are distributed under version 1.0 of the Boost Software License, as described at the top of each file and reproduced here below. Note that I have waved all copyright to the Derelict source, so no copyright attribution need be given.
+
+Boost Software License - Version 1.0 - August 17th, 2003
+
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+
+===============
+
+The audio files found in the ./bin/audio directory are distributed under the terms of the respective licenses of the original source files.
+
+"buzzer.wav" was cut from the original source file "buzzer.wav" at http://www.freesound.org/people/guitarguy1985/sounds/54047/
+
+"click.wav" is renamed from the original source file "mouse click.wav" at http://www.freesound.org/people/THE_bizniss/sounds/39562/
+