Adding use_proxy to curlconverter

[PhilippWillroth]

Hi, really appreciate this package. It helps a lot setting up a script to pull data from the web.

Unfortunately in my company we use a proxy server. HTTR provides for this cases the use_proxy argument. In order to use the function provided by make_req I have to change the function manually. Is there a way to add this functionality? Maybe by expanding the straighten function, so that you can add additional parameters such as use_proxy?