Trivial Local File Import

[georg-schwarz]

Explores technical implementations of #474.

Introduces a trivial file import mechanism.
All elements of files are exported (thus "trivial").

TODOs

• adjust to whatever syntax [RFC] Exports, Imports, and Libraries #474 will settle on
• fix tests
• add documentation
• ensure the mechanism works when starting the interpreter from different locations (not only within work dir)
• check whether transitive imports are working

Next steps

• limit accessible elements to ones that were made accessible explicitly (e.g., export keyword)