fix non-ascii character encoding problem

- tornado.web.RequestHandler.get_argument returns a unicode string.
  And urllib.urlencode converts unicode chars into string chars
  before percent-encoding them.
  If an argument contains non-ascii characters, encoding(default
  charset is system dependent) results in UnicodeEncodeError.
Merge pull request #3 from quiver/ch5_urlencode

fix non-ascii character encoding problem