Grumpy to-do list:
 - add "if-unmodified-since:" and "if-modified-since:" support (412 & 304 codes)
 - add "Last-Modified:" header whenever possible
 - add MD5 computation function (would be used for MD5 header and digest auth)
 - add support for the digest auth mode
 - MD5 header for small (=<1M) files
 - Add content-lenght for all responses (not only 200)
 - Set AUTH_USER and REMOTE_USER variables when running an authenticated CGI application
 - Add a way to create Gopher links to other Gopher servers
