* Enable compiling vweb with -prod (by supressing 'declared and not used' warning about 'reset') .
* Fix http responses (now wrk is happy and shows no errors) by adding a Content-Length header.
* Fix -g compilation for urllib.v .
* vweb: println action= only in debug mode.
* vweb: max request headers counting fix.
* Make vweb.html get a 'ctx mut Context' param, just like the other methods.
* vweb: simplify add_header.
* Use a string builder for the most common html case so that the response http text can be send in one go.
* vweb: reduce _STR/string interpolation usage in the most common html response case.
* vweb: refactor common http response formatting into Context.send_response_to_client/2 method.
