Simple request URI modification logic

[awiejacha]

This small code gives opportunity to 'intercept' and modify request URI on-the-fly. When application is used to crawl/visit over resources, making request in the automated way, in some cases it is needed to modify uri/querystring, basing on some rules - e.g. we know that for specific location additional querystring or chunk of path needs to be appended/removed.

Additionally, fixed a bug with resp.cookies being undefined if follow_set_cookies is enabled and previous response cookies not present and set-cookie headers is not present.

[tomas]

Looks good but I'd try to use a more descriptive method for the option. Something like uri_modifier perhaps?

[awiejacha]

Sure - just 5 chars more and much more description.

[tomas]

OK would you update your PR?

[awiejacha]

Updated. Thanks for keeping eye on this!