Environs

- `EnvError` subclasses `ValueError` ([50](https://github.com/sloria/environs/pull/50)).
Thanks [alexpirine](https://github.com/alexpirine).
- Test against Python 3.7.

- Use python-dotenv for parsing .env files. `Env.read_env` behaves
mostly the same except that a warning isn't raised by default if a
.env file isn\'t found. Pass `verbose=True` to raise a warning.

Features:

- _Backwards-incompatible_: `Env.read_env` raises a warning instead of
an error when `.env` isn\'t found
([10](https://github.com/sloria/environs/issues/10)). Thanks
[lachlancooper](https://github.com/lachlancooper) for the
suggestion.
- Add optional Django support. Install using
`pip install environs[django]`, which enables `env.dj_db_url` and
`env.dj_email_url`.

Features:

- Fix compatibility with marshmallow 3 beta.

Features:

- Add recurse parameter to Env.read_env
([9](https://github.com/sloria/environs/pull/9)). Thanks
[gthank](https://github.com/gthank) for the PR.

Features:

- Add support for nested prefixes
([8](https://github.com/sloria/environs/pull/8)). Thanks
[gvialetto](https://github.com/gvialetto) for the PR.

Other changes:

- _Backwards-incompatible_: Drop support for Python 3.3 and 3.4.