[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#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

[Issue#81]: Now that all the variables have the correct module assigned, this member can be used safely.

i[Issue#81]: When a real has been declared without prec specification, we suppose is a single prec real

[Issue#81]: Old pattern was matching with function_somthing, i.e. with lines that were not containing functions declarations