Support libraries in different directories

[EvanMachusak]

e.g., if I open a root folder called "CQL" in VSCode with a structure like this:

• CQL
  • FolderA
    • LibA.cql
  • FolderB
    • LibB.cql
  • FolderC
    • LibC.cql

I should be able to include LibA from LibB.

Currently the extension relies on requiring colocation of all CQL to prevent the possibility of ambiguity. I think it's acceptable to display an error if the library identifer and version in LibA.cql and LibC.cql are the same (thus creating an ambiguous reference).

It would be nice if the cql-to-elm CLI supported this too.