Bump to version 0.4.

Changelogs:
* Major CSS cleanup.
* Reworked grid layouts, added a new feature to "push" columns.
* Updated readme.
* Added some more elements into the test page.

TODO:
* Add all of the remaining grids, from 1-12.
* Simpler class system for columns.
* (Long-term) Working GitHub page with all the required docs.