Document common patterns using Hologram

Read [Hologram](https://github.com/trulia/hologram) formatted comments in Sass stylesheets (currently those saved under /stylesheets/common/modules) and generate a style guide that lives within /docs/styleguide/.

The following styles have been documented as a test sample:
* charts/_doughnuts.scss
* facia/_pagination.scss
* _media.scss
* _social.scss
* _stars.scss
* _tabs.scss
* _tag.scss

## Known issues/questions:
* Index page is given the wrong title (‘Facia’, rather than ‘Charts’). This is a bug in Hologram, I think.
* Currently, any components that require JS to fully function, don’t (tabs for example).
* Templates mimic the structural HTML of the website. Without being tied to the Scala templates, these will likely break without continued maintenance.
* Mixing section front and article components on the same page is problematic as they use different breakpoints and appear within different structural layouts.
* Requires the HTML to be written twice, which isn’t very DRY.
* In the first set of styles I’ve documented, I’ve omitted `js-` classes, and `data-` attributes. Is this the right approach?

Idea is to live with this, and then adapt and improve where we see issues.
Would it be appropriate to only compile the style guide in dev mode? then you could do `grunt watch:css --dev`