Add Spress

Spress is a static site generator which allows you to write and publish your web sites.

README.md

 
 * [Sculpin](http://sculpin.io) - A tool that converts Markdown and Twig into static HTML.
 * [Phrozn](http://phrozn.info) - Another tool that converts Textile, Markdown and Twig into HTML.
+* [Spress](http://spress.yosymfony.com) - An extensible tool that converts Markdown and Twig into HTML.
 
 ## HTTP
 *Libraries for working with HTTP and scraping websites.*