Resolve "Simplified dependency specification"

What does this MR do?

See #52 (closed).

Changes to public APIs

Adds a shorthand syntax for dependencies. This is backwards-compatible.

Author's checklist (required)

• If the nitrile.yml format has changed, a migration has been defined in Nitrile.Package.Migrate
• If bugs have been solved, tests have been added (guidelines)
• A changelog entry has been added (guidelines)
• Newly added code is documented (guidelines)
• Newly added code has a style consistent with the rest of the repository
• Intermediate commits compile (use git rebase -i main if not)

Related issues

Closes #52 (closed)