refactor: now, usernames can contain only alphanumeric characters

feat: added username validation to validator service

feat: added username validation to validator service

feat: added password validation to validator service

* Added password validation to validator service
* Added Birthdate and password validator options

refactor: removed error return parameter from validator service's Ema…

…il and Birthdate functions

test: set the auxiliary validator function as a variadic parameter

test: added an auxiliary validator function to the CreateValidateFn

feat: added Email and Birthdate functions to validator service (again)

refactor: added nil mapper checker on CreateValidateFn

refactor: substituted validations service's Validate function by Crea…

…teValidateFn