Skylib module containing rules to create metadata about subdirectories.
## subdirectory
subdirectory(name, parent, path)
**ATTRIBUTES**
| Name | Description | Type | Mandatory | Default |
| :------------- | :------------- | :------------- | :------------- | :------------- |
| name | A unique name for this target. | Name | required | |
| parent | A label corresponding to the parent directory (or subdirectory). | Label | required | |
| path | A path within the parent directory (eg. "path/to/subdir") | String | required | |