Added "automapping" feature for environment variables

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes

For more details, see [README.md](https://github.com/phansys/ParameterHandler#using-same-names-for-parameters-and-environment-variables).