Add circle CI testing in the template

I’ll be nice to could select circleCI (http://circleci.com/) as the CI service of the template

$ cookiecutter https://github.com/pydanny/cookiecutter-django
...

Select Continuum integration service:
1 - Travis CI
2 - CircleCI
Choose from 1, 2 [1]: 1

And seleting 2 will generate a circle.yml with a basic configuration

If this feature is approved I could provide a PR with the change.

[sfdye]

@timmyomahony here you go, sample CircleCi config with codecov support.

version: 2
jobs:
  build:
    working_directory: ~/app
    docker:
      - image: circleci/python:3.5.4
        environment:
          DATABASE_URL: YOUR_DATABASE_URL
      - image: circleci/postgres:9.6.2
        environment:
          POSTGRES_USER: postgres
          POSTGRES_DB: postgres
    steps:
      - checkout
      - restore_cache:
          key: deps1-{{ .Branch }}-{{ checksum "requirements/test.txt" }}
      - run:
          command: |
            python3 -m venv venv
            . venv/bin/activate
            pip install -r requirements/test.txt
      - save_cache:
          key: deps1-{{ .Branch }}-{{ checksum "requirements/test.txt" }}
          paths:
            - "venv"
      - run:
          command: |
            . venv/bin/activate
            py.test --cov=./
            codecov --token=token
      - store_artifacts:
          path: test-reports/
          destination: tr1

[sfdye]

@timmyomahony Is because travis is not free for our private repo, circle is free for one concurrent build.