New features
* Add `emap` ([doc](http://owlmixin.readthedocs.io/en/stable/api/owlcollections.html#owlmixin.owlcollections.TList.emap))
* Add `partial` ([doc](http://owlmixin.readthedocs.io/en/stable/api/owlcollections.html#owlmixin.owlcollections.TList.partial))
* Add argument `first` which can select concat direction ([doc](http://owlmixin.readthedocs.io/en/stable/api/owlcollections.html#owlmixin.owlcollections.TList.concat))