Add SASS Styles

I have optimized joyride for a new build system, [gulp](http://gulpjs.com/), as well as converted fixed and static CSS styles to SASS styles.

All proportions, lengths, widths, colours, and behaviours can now be adjusted in the ``joyride_variables.scss`` file.

The SASS can then be compiled using the ``sass`` task which I created for gulp:

```
gulp sass
```

No changes were made to the javascript file, except tidying it up for consistency.

I also updated the directory structure.

I encourage you to merge this PR, as I feel it greatly increases the usability of joyride.