Since there is no established format for representing collections within env variables, to enable their support, the feature with a custom parser attribute added.
Add helpers for parsing env variables into collections
Improve rustdoc for `env_utils` functions
Improve `parse_env` example
This gets rid of a lot of duplicated logic that was previously
copy&pasted. This commit alos:
- Makes it easier to implement new formats
- Gets rid of a few bugs
- Makes the system more flexible (more options)
- Adds a lot of additional tests