Support inlining favicon

[stonio]

Cannot inline PNG favicon because the ouput HTML tag is not correct:

• rel="icon"is omitted
• hrefattribute replaced by src

Input HTML tag:

<link rel="icon" type="image/png" href="img/favicon.png" inline />

Actual result:

<link type="image/png" src="data:image/png;base64,XXXXX..." />

Expected:

<link rel="icon" type="image/png" href="data:image/png;base64,XXXXX..." />