0.21    Wednesday, 11 September 2015
        Using 'Scalar::Util::reftype()' instead 'ref()'.

0.2     Wednesday, 10 September 2015
        Added new functions 'every_keys' and 'some_keys'.

0.02    Monday, 16 Mar 2015
        Renamed 'is_exists' to 'key_exists'.

0.01    Sunday, 15 Mar 2015
        First version, released on an unsuspecting world.