Fix type hinting for load_env (#2107)

* Deprecate `load_env` in favor of `env_prefix`

`load_env` both enabled/disabled environment variable parsing, while
also letting the user modify the env prefix. Deprecate the ability to
disable environment parsing, and add a new config variable to track the
user's desired prefix for environment-based configuration.

Resolves: #2102

* Add a few common .gitignore patterns

.gitignore

@@ -18,3 +18,6 @@ build/*
 .DS_Store
 dist/*
 pip-wheel-metadata/
+.pytest_cache/*
+.venv/*
+.vscode/*