url: improve url.parse() performance

This commit improves url.parse() performance by 50-210%
with the existing url/url-parse benchmarks. Also, the
optimizations made in url.format() result in a 40%
increase in performance for url.resolve().

Some optimization strategies used in this commit include:
* Combining multiple searches on the same string into a
   single loop
* Avoiding unnecessary string.split() and array.join()
* Minimizing creation of temporary strings
* Using a faster alternative to encodeURIComponent,
   borrowed from the querystring module