Remove tests temporarily.

Re-add them later when we have a stable API.
Add another CPP code example: purefac which performs no I/O.
Make the interpreter work with the Core language.
Add -i (--interpret) mode to cpp.

When -i option is given, cpp interprets the program instead of compling it.
Add Show instance declaration of Value.
Add a CPP code example to test || operator.
Remove VTrue and VFalse and use VInt 1 and VInt 0 instead.

The Core language does not support bool type.