Allow clarifying different versions of the same crate separately

[liss-h]

Is your feature request related to a problem? Please describe.
When there are duplicate dependencies with different versions in the tree and cargo-about is not able to correctly determine the licensing situation it would be nice if we could clarify both versions of the crate separately in case they have slightly different licensing situations.

Describe the solution you'd like
Allow (optionally) to specify a version on the clarification.

Examples of how this could look like:

• [crate.'0.1.0'.clarify]
  license = "..."
  
  [[crate.'0.1.0'.clarify.files]]
  # ...

• ['crate-0.1.0'.clarify]
  license = "..."
  
  [['crate-0.1.0'.clarify.files]]
  # ...