add support for composed fonts using quotes like "New Times Roman"

[RomiPierre]

Composed fonts like "New Times Roman" and others fonts using quotes in style sheets are generating an error during parsing styles.

Sample

[tobio]

I can't reproduce this error. Premailer appears to be behaving correctly with the below markup

<style>div { font-family: "New Times Roman" }</style>
<div></div>

[martinnormark]

I tested this since the introduction of AngleSharp in #76, and it now works.

The markup and CSS above produces the following when inlined, which is valid: http://stackoverflow.com/a/5352973/2972

<div style=\"font-family: &quot;New Times Roman&quot;\"></div>