Adds a part of response header before response body

In file maid.asd: Adds the 3rd-party library local-time into dependencies and updates the version.

In file README.md: Adds some details for TODO entry *response header* and tags a part of them with STRIKE tag, since they're implemented.

In file maid.lisp: In function HELLO-REQUEST-HANDLER, adds some calls of FORMAT to output the response header, fields include Date, Connection, Server and Content-Type. The placeholder '~%' means #\Newline and I choose this character for making the DRAKMA HTTP clien and Firefox recognizes the response from the web server.