YAML mapping keys for item identifiers instead of "id"

[grahamdyson]

Items in Eunice YAML are either represented by just their identifier or a mapping that includes the identifier as an id key.

- item 1
- id: item 2
  dependsUpon: item 1

It might be possible to improve readability for items by using a mapping key to represent the identifier with other properties for that item as another mapping in the value.

- item 1
- item 2: { dependsUpon: item 1 }