Enable setting headers and query parameters. Also add 'fake extensions' mechanism.

[laundmo]

This PR adds 3 features:

• Headers
• Query params
• ability to use URLs which don't end in a file extension, by adding a "fake" extension with 2 dots: ..png which will be stripped for the actual request

nice to have: example showcasing this. not sure how to do that, as the whole idea of this is to allow authentication in the requests

supersedes:

• #24