we need to add a license

see the blog post by Jake VanderPlas

http://www.astrobetter.com/blog/2014/03/10/the-whys-and-hows-of-licensing-scientific-code/

I propose we license the package with a BSD-like license. We need to add the license text in a LICENSE file and commit it to the repo. While we are at it maybe we should add a Authors or Contributers file as well.
