Add a check in the interpreter's class creation path that detects when a user-defined class attempts to inherit from any of the seven built-in types (Class, Fiber, Fn, List, Map, Range, String). When such an inheritance is detected, a runtime error is raised with a descriptive message indicating the class name and that it may not subclass a built-in. This implements the restriction discussed in issue #70.
Also adds test files for each built-in type to verify the runtime error is correctly triggered, and includes a commented-out test for closure subclassing that currently causes a segfault.
Extend the Makefile to produce both static (.a) and shared (.so) library variants for debug and release configurations, updating the clean target and .gitignore accordingly.
Peter Reijnders