Implemented most of the interpret stage of the interpreter. Added some exception classes and the different environment/store classes and their subclasses. Added some tests for the interpreter. Still may need to refactor the tokenize, parse, interpret and all test methods based on a changing understand of how things should work. Tests do not work right now. In the process of refactoring them.
Previous commit message applies to this one.
Refactored all binary operations and moved logic into a separate method, which condensed the code and made it DRY-er.
Finished writing all the tests. Fixed recursion. Interpreter is functional and complete.