Move to Circle CI

[rpkilby]

The overall goal of the PR is to move off of Travis and onto CircleCI. In part, this is because our org privileges don't allow Travis to push status updates on PRs/commits.

There are also several supporting changes that update packaging/distribution and testing. I've tried to keep the commit history fairly straightforward, and can go into more depth. The highlights are:

• Add tox, a local CI runner. It allows you to define a test matrix (e.g., test against these several versions of Django & DRF), and manages setting up the test environments. Basically, it's no longer necessary to manage the dependencies.
• Move tests outside of the package, since it isn't necessary for tests to be installed to a user's environment. Note that the sdist still include the tests/docs/etc, although they aren't installed.
• Move package metadata out of setup.py and into setup.cfg (more info)
• Fix tests for Django 2.1 & 2.2 (note that more errors are logged in the test output for these versions, but I think these are expected responses e.g., expected login failures).

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@624ad01). Click here to learn what that means. The diff coverage is 100%.

[rpkilby]

I think this is ready for review. Note that coverage is reduced a bit, for two reasons:

• tests were previously included in the numbers, bumping the total percentage
• branch coverage has been enabled, and some lines are only partially covered

[BarnabasSzabolcs]

Hi, as a user of rest-auth, thanks for the contribution! This repo is not maintained anymore, so the development moved to dj-rest-auth. (reference: https://github.com/Tivix/django-rest-auth/issues/568) It may be best, if you move this PR there. (and upgrade to using dj_rest_auth)

new repo link: https://github.com/jazzband/dj-rest-auth (I'm not the upkeeper of that repo, it just makes sense for me to help you merge your PR)

Many Thanks, Barney