Environs

Bug fixes:

- Handle JSON decoding errors when using `env.json` ([212](https://github.com/sloria/environs/pull/212)).
Thanks [bvanelli](https://github.com/bvanelli) for the PR.

Bug fixes:

- Apply variable expansion to default values ([204](https://github.com/sloria/environs/pull/204)).
Thanks [rjcohn](https://github.com/rjcohn) for the PR.

Deprecations:

- Rename `subcast_key` argument of `env.dict` to `subcast_keys`
for consistency with `subcast_values`. `subcast_key` is deprecated.

Features:

- Add time parser ([191](https://github.com/sloria/environs/issues/191)).

Features:

- Add `enum` parser ([185](https://github.com/sloria/environs/pull/185)).
- Add `delimiter` param to `env.list`
([184](https://github.com/sloria/environs/pull/184)).

Thanks [tomgrin10](https://github.com/tomgrin10) for the PRs.

Bug fixes:

- Loosen `ParserMethod` typing ([186 (comment)](https://github.com/sloria/environs/issues/186#issuecomment-723163520)).
Thanks [hukkinj1](https://github.com/hukkinj1) for the PR.

Other changes:

- When using deferred validation (`eager=False`), parser methods return `None`
for missing or invalid values.
_Note_: This may break code that depended on parser methods returning `marshmallow.missing`,
but this behavior was not documented nor tested and therefore is not considered public API.

- _Backwards-incompatible_: Rename `subcast` param of `env.dict` to `subcast_values` for consistency with `subcast_keys`.
- _Backwards-incompatible_: Remove variable proxying. Use variable expansion instead (see 8.1.0 release notes below)
([175](https://github.com/sloria/environs/issues/175)).
- _Backwards-incompatible_: Drop support for marshmallow 2 and Python 3.5,
which are both EOL ([174](https://github.com/sloria/environs/issues/174)).