Create new Jekyll site.
Various changes.

Various changes, including:

* Add Sass configuation file.
* Convert CSS stylesheets to Sass stylesheets.
* Add images from the MiniCard WordPress theme.
* Modify Sass stylesheets to use the images from MiniCard.
* Modify `default` Jekyll layout HTML to use the new Sass stylesheets.
Vertically center the elements in the header.