This issue propose 2 features:
- 
Add support for "convenio" in "boleto" validator, since it related formatter (format-boleto) supports "convenio"
 
- 
Returns which partial is wrong in is-valid-boleto. To avoid break the current contract, we could just add a second parameter, that will be a flag to turn on this feature.
 
I could work on both, just checking if are valid features