Include author/license in the distribution

[brodycj]

I needed to use your wonderful library for a client and had to add a section to the project's README.txt to track the source of promise-7.0.4.min.js before it is forgotten. It would be really helpful if the author/copyright/license info would be part of the distribution files (promise-?.?.?.js, promise-?.?.?.min.js, promise-done-?.?.?.js, promise-done-?.?.?.min.js, ...). Here are a couple of examples:

• https://github.com/MrRio/jsPDF/blob/master/dist/jspdf.min.js
• https://github.com/macek/jquery-serialize-object/blob/master/dist/jquery.serialize-object.min.js