Get url-encoding working

[jyn514]

[jyn514]

This will be a pain because then we have to treat URLs as arbitrary binary instead of strings (because /%00blah.pdf) is a valid url

[jyn514]

I think adding an explicit length parameter for the url is the way to go. That means we can't use string library functions for the url. Would be nice to know if nulls are allowed or if we can just strip them.