Emacs mode improvements

I'd like to see julia-mode.el available on [MELPA](http://melpa.milkbox.net/), which is the largest package manager for Emacs packages.

In order to do that, julia-mode.el needs to conform to the standard layout for Emacs packages. This is the first commit. I also fixed a few minor issues I encountered.

Let me know if there are any changes you'd like in order to merge this.