All toString methods now return a Ptr<LispObject> of Type::String.
Implemented cont::toString.
Implemented env::toString.
Implemented lambda::builtin::toString.
cont::toString now return "<continuation>" instead of "#continuation".
Implemented unit test for nil::toString.
Implemented number::toString.
Implemented overload for typeCheck function, which takes a second Type argument to check against if the type of the object is not of the first type argument.