Add continuous integration (Travis CI)

[sdhutchins]

Check out python-poetry/poetry#366

[sdhutchins]

Start with:

language: python
python:
  - 3.5
before_install:
- pip install poetry
install:
- poetry install -v

[sdhutchins]

A full example (https://wrongsideofmemphis.com/2018/10/28/package-and-deploy-a-python-module-in-pypi-with-poetry-tox-and-travis/):

language: python
python:
- '2.7'
- '3.5'
- '3.6'
matrix:
  include:
  - python: 3.7
    dist: xenial
before_install:
- pip install poetry
install:
- poetry install -v
- pip install tox-travis
script:
- tox
before_deploy:
- poetry config http-basic.pypi $PYPI_USER $PYPI_PASSWORD
- poetry build
deploy:
  provider: script
  script: poetry publish
  on:
    tags: true
    condition: "$TRAVIS_PYTHON_VERSION == 3.7"
env:
  global:
  - secure: [REDACTED]
  - secure: [REDACTED]