CSS quotes, width attributes, readme fix

@guille 

Three small things in this PR:
- updated learnboost to automattic in readme because some paths, like build status, were broken
- preserve single quotes where meaningful instead of converting everything to double quotes
- add an option to apply width attributes to certain elements, this makes inlining for email clients that don't respect widths set in CSS much easier

Please see individual commit messages for more details.

This will bring the automattic version almost up to where the forks are at. The other important changes relate to how the stylesheets get pulled in from links, and I know we want to pull that out of core and make it a separate library.