Added several stuff:
Added several stuff:

* A new ast type called A_BOOLEAN_OPERATOR
* A new whole enum to identify types of boolean operators called
boolean_operator_type.
* Added struct for the node_boolean_operator and the init and free
methods.
* Added an auxiliar method to help get the right boolean_operator_type
from a token_boolean_op.

maitesin/acc,maitesin/acc