Global variables

Created by: jacosro

Static attributes of each class are represented as global variables. This means that each method declaration will have a global_formal_in and global_formal_out parameter for each one of the global variables of the program (static attributes of every class). Consequently, every method call will also have global_actual_in and global_actual_out nodes for each global variable.

Four new NodeTypes must be added: GLOBAL_FORMAL_IN, GLOBAL_FORMAL_OUT, GLOBAL_ACTUAL_IN, GLOBAL_ACTUAL_OUT, in order to be able to distinguish them from normal parameters.

@cargaji What do you think?