Renamed LICENCE file to LICENSE

Renamed LICENCE file to LICENSE which is consistent with content, see first line of the file itself :-)

Obviously, this is just spelling; and the fact is that (in en_GB) both are probably correct for the file name (enjoy reading http://www.grammar-monster.com/easily_confused/licence_license.htm and http://en.wikipedia.org/wiki/License); in en_US it would however be LICENSE and since the first line reads "The MIT License (MIT)", this seems the obvious for this project.

However, I don't really care myself (and I'm not a native English speaker); so feel free to ignore and get a life.