Get logical imports in "wren_modules" working.

There's a lot of changes here and surely some rough edges to iron out.
Also, I need to update the docs. But I want to get closer to landing
this so I can build on it.

test/language/module/compile_error/compile_error.wren

@@ -1,2 +1,2 @@
 System.print("before") // expect: before
-import "./module" for Module // expect runtime error: Could not compile module 'test/language/module/compile_error/module'.
+import "./module" for Module // expect runtime error: Could not compile module './test/language/module/compile_error/module'.