Redirect /job to / and /job/:job/build to /job/:job #104

replaces #81

A single potential change depending on semantics of Dream.to_form_urlencoded

There's a corner case not handled correctly, but I think this is good to merge and we can fix that later

     let parent = parent ^ "/" in
     let url = match Dream.queries req with
       | [] -> parent
       | xs -> parent ^ (Dream.to_form_urlencoded xs)

     let url = match Dream.queries req with
       | [] -> parent
       | xs -> parent ^ "?" ^ (Dream.to_form_urlencoded xs)
     in