The term data: URL refers to URLs that use the data: scheme. [RFC2397]
http://tools.ietf.org/html/rfc2397
Syntax：
dataurl := "data:" [ mediatype ] [ ";base64" ] "," data
mediatype := [ type "/" subtype ] *( ";" parameter )
data := *urlchar
parameter := attribute "=" value
example：
data:text/html, <div></div>
