Documentation

Find and warn on:

• Unused import statements (qualified or unqualified)
• Unused references in an explicit import list
• Implicit imports of modules
• Implicit imports into a virtual module (unless the virtual module only has members from one module imported)
• Imports using hiding (this is another form of implicit importing)

A sum of the possible name types, useful for error and lint messages.

Map of module name to list of imported names from that module which have been used.