Upgrades bootstrap to version 3. Need to fix some styling as a result.
Switches 'span' to 'col-md-x' since 'span' was removed in Bootstrap 3.
Starts to reimplement the styleguide according to Bootstrap 3 standards.
Will finish when there's time or when necessary to implement new content. Fixes #29.
Merge pull request #30 from WGBH/upgrade-bootstrap

Upgrade bootstrap