Allow user to choose how links are extracted from responses

[inglesp]

We currently extract links from HTML by looking for src and href attributes, and from CSS by looking for @import rules and URI tokens.

A user might want to extract links from other places, such as data- attributes in HTML, or values in JSON objects.

We should find a way to allow the user to configure how links are extracted from responses.

[shahzeb1]

I would like to tackle this issue. 😃