1. Fixed bugs in compile_to_c(), also added assert.
2. Completed refactoring of code for reuse from generated C code
3. #ifdef to handle GUI mode for a global definition
4. If exception occurs before core library has been loaded, exit.
5. All closures now compiled to native code at the time of definition.
6. Because of #5 above, expressions cannot refer to closures not yet defined (bummer). utils.lisp and unit_tests.lisp modified accordingly.
7. All functions inside generated C code will return unsigned int.