Split source into multiple files, should ease further development

Hi there!

I started today diving into grex's source code and I thought that it could benefit being split into multiple files. I believe this change in grex should make it easier for others (including me :P) to send pull requests in the future.

I basically extracted gremlin.js and transaction.js out of the main file.

I did so in order to start sending pull requests as I continue developing Mogwai.

Let me know if you're fine with the way it currently looks. Note that I also fixed a few issues with semicolons, spaces/tabs and such.

Cheers,