Ref: 1adf29af13
BREAKING CHANGE: img[src] URLs are now sanitized via a separate
whitelist regex instead of sharing the whitelist regex with a[href].
With this change, img[src] URLs may also be data: URI's matching
mime types image/*. mailto: URLs are disallowed (and do not make
sense for img[src] but were allowed under the a[href] whitelist used
before.)