Django-s3file

* Fix content-type POST conditions (83)

* Move readme from Markdown to reStructuredText

* Remove Django 1.8 & 1.10 support
* Add Django 2.0 support
* Assign string value to hidden input (81)
* Add event listeners in favor of overloading attributes (80)
* Remove submit logic from click event handler (79)

* Fix -- Add multi mimetype support for accept attr

* Fix -- Pass submit value to backend