Django-stdimage

**BREAKING CHANGE**

* Remove upload_to utils in favor of [django-dynamic-filenames](https://github.com/codingjoe/django-dynamic-filenames).

* Add option to management command to ignore missing file (191)

* Fix log statment -- Use __mod__ over format style (190)

* Add process_variation classmethod to simplify customization (188)

* Circumvent "OSError: image file is truncated" issue. (184)

* Refactor tests to increase coverage
* Refator rendervariations command to use concurrent.futures
* Update badges
* Switch from coveralls to codecov
* Remove Django 1.8 & 1.10 support
* Remove Python 2 support
* Add Django 2.0 support
* Switch to pbr for releases
* Update coverage from 4.4.1 to 4.4.2
* Ignore all missing doc strings
* Update README.md
* Update pytest from 3.2.2 to 3.2.3
* Update tox from 2.8.2 to 2.9.1
* Update tox from 2.8.1 to 2.8.2
* Update pytest from 3.2.1 to 3.2.2
* Update tox from 2.8.0 to 2.8.1
* Update tox from 2.7.0 to 2.8.0
* Update pytest from 3.2.0 to 3.2.1