Parse image tags

[Kleissner]

The crawler should optionally parse image tags that are in the form <img src="..."> and use it as input for crawling (just as it would consider <a src=""> links to images).

I'm creating a pull request which implements that in a few lines.

[moredure]

you can add area, frame, iframe, ilayer, layer parsing as well

[moredure]

as well as link