Gets a URL for a key.

def make_key_url(self, key):
        """Gets a URL for a key."""
        if type(key) is bytes:
            key = key.decode('utf-8')
        buf = io.StringIO()
        buf.write(u'keys')
        if not key.startswith(u'/'):
            buf.write(u'/')
        buf.write(key)
        return self.make_url(buf.getvalue())