[Issue#81]: Now pointer to functions are correctely traced. Fix for dimension function and logical var.

[Issue#81]: Refactor of MainFunction, things were scattered all over. Now use statement is correctly propagated, then var are added right away to public

[Issue#81]: Derived_types members should not be added to the main sbr, instead they have to appear in vault.variables array

Issue#83

See merge request otinto/AutoRPE!14

[Issue#81]: Changed the way in which variables are added to structures: a new variable was created, which was not only unnecessary but wrong since some properties were lost. Some refactoring for the errors.

[Issue#81]: This way of discarding variables not used is failing when function are nested, or there is declaration of interfaces