feat(coding-style): Add editorconfig for consistent coding style

More info at http://editorconfig.org/

* The list of projects already using it to standardize their coding
styles[1].

* Inspired by editorconfig of django-model-utils[2].

[1]: http://git.io/pz1vWA
[2]: http://git.io/QIAWvw
chore(requirements): update pip requirements to latest stable.