Now struct Node is class.
Now the second member of the structure Token is a pointer to class Node.
Added a new constructor and the old constructor was modified. Added CallFunction(), ProcessingFunctions(), SolvesSimpleComputation(), AddStandardFunctions() and were made other small modifies.
Added new methods in class.
Modified the calls at struct Node because now struct Node is class Node.
Modified some declarations from class Tree because now struct Node is class Node.