Add new directory structure handler

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Fixed tickets | #117
| License       | MIT

This is a first move toward https://github.com/symfony/symfony-standard/issues/584
This allows the use of the new directory structure (not by default).

Hm since bins are only installed when the corresponding package actually gets updated, it might not always be available.