some code clean up

Hey guys!

First of all, just want to say thank you for creating such an amazing framework. I'm currently working hard to become a full-stack javascript developer and have been recently learning express.

While reading through the code many times, I noticed some inconsistencies in the formatting (especially with the "Module Dependencies") and thought it could be a chance for me to try and become involved in open source. In this commit I formatted the "Module Dependencies", moved the export to the top with comments, and added comments to the initialize function for Layer. 

If this is not acceptable please let me know if I can help out in any other way. I am willing to go through all files and format "Module Dependencies" or any other mundane tasks you need completed. Thanks so much for reading—I am greatly inspired by you all!