fix functions with global vars (test5). all tests from part 3 work except test13, function side effects
add create_instance_env function, but not fully complete
interpret the class declarations properly
put the class variable containing all classes in the bottom layer of environment
final class environment is set up with addition of boxes
began to add functionality for methods returnning a value
use single interpret_function for getting value/environment
inheritance and add new operator
more inheritance functionality and add tests from part 4