Added parameterized URL capability

I added the ability to parameterize GET and POST requests via parameter tags (e.g., $1, $2) embedded in the targetUri string. These can be filled in by including matching "proxyArg1", "proxyArg2", etc. HTTP parameters in your URL query string.  (They must be in the query string, even for post, because I had to parse them manually, in the Servlet; calls to getParameter() consume the content InputStream, which messes up the proxy of the content to the downstream server.) I attempted to ensure this is backward compatible, even with subclass extensions.