envsubst Python Library

The `envsubst` library for Python provides functionality to substitute environment variables in a string, mimicking the behavior of the GNU `envsubst` command-line utility. It supports `$VAR` and `${VAR}` style variable expansions, including the use of default values like `${VAR:-default}`. The current version is 0.1.5, with its last release in October 2019, indicating a maintenance-only or inactive development cadence.