Support data urls for images#30

Example: the Markdown input is

The expected output is:

<img alt="With data URL" src="data:image/svg+xml;base64,PHN2ZyB3aWR0aD0iMzAwIiBoZWlnaHQ9IjIwMCI+CjxjaXJjbGUgY3g9IjUwIiBjeT0iNTAiIHI9IjUwIiBmaWxsPSJyZWQiIC8+Cjwvc3ZnPg==">
The actual output:

<img alt="With data URL" src="#harmful-link">

Embedding images in data urls turns the database into image storage, which it’s not suited for. Instead upload an image or link to it using the standard ![Image title](image-link)