Optenum

- add choices() classmethod to Options for django choice filed.

* do not convert Option.text to string any more due to gettext_lazy in django reason.

**Full Changelog**: https://github.com/samuelchen/optenum/compare/v1.1.6...v1.1.8

(should be at Jun 04 2019)

* support + (plus) for Group

**Full Changelog**: https://github.com/samuelchen/optenum/compare/v1.1.5...v1.1.6

* Fix issue of creating single option group as class attribute

* Fix option not found issue when creating option group as class attribute (class attributes creation is not in order)
* Fix option attributes order in python 3.4 & 3.5

* Tagged option group support construct as class attribute and support +, -
* fix "random ordered options in group" issue
* fix "tag name checking" issue