* Add 'expor env' dummy command
* (WIP) Abstract away module exportables as Overlay
* Switch to Overlays for use/hide
Works for decls only right now.
* Fix passing import patterns of hide to eval
* Simplify use/hide of decls
* Add ImportPattern as Expr; Add use env eval
Still no parsing of "export env" so I can't test it yet.
* Refactor export parsing; Add InternalError
* Add env var export and activation; Misc changes
Now it is possible to `use` env var that was exported from a module.
This commit also adds some new errors and other small changes.
* Add env var hiding
* Fix eval not recognizing hidden decls
Without this change, calling `hide foo`, the evaluator does not know
whether a custom command named "foo" was hidden during parsing,
therefore, it is not possible to reliably throw an error about the "foo"
name not found.
* Add use/hide/export env var tests; Cleanup; Notes
* Ignore hide env related tests for now
* Fix main branch merge mess
* Fixed multi-word export def
* Fix hiding tests on Windows
* Remove env var hiding for now
