release 0.0.6.

Squashed commit of the following:

commit f9b0f9c3412778a83ba6e68f5d3155cb31ea2408
Author: HARUYAMA Seigo <haruyama@unixuser.org>
Date:   Fri Jan 31 18:52:59 2014 +0900

    Add a description

commit c91186e34a7f8b49dfdf99fa760f8251b1b1b445
Author: HARUYAMA Seigo <haruyama@unixuser.org>
Date:   Fri Jan 31 18:48:03 2014 +0900

    Add referers_yaml and encodings_yaml attributes.