Use Unlicense instead of MIT

[balupton]

As this is just a skeleton that other people will take and redo, it would be nice if it was in the public domain, so we don't have to worry about giving attribution to files that we have modified - say even files we haven't.

http://spdx.org/licenses/Unlicense.html

[harlantwood]

CC0 is also a nice way to do that.