Add support/tests for $redis->psubscribe.
Naming/documentation tweaks.

    - Rename Mojo::Redis::Subscription->subscription_type to type.
    - Fix POD examples with psubscribe/subscribe to disregard 'on' return value.
Update Changes for 0.9916.
Merge pull request #20 from kanatohodets/psubscribe

Add support for $redis->psubscribe.