* t/11-empty_record.t: creating and testing what happen when the record is empty
* lib/Biblio/Record/USBC.pm: refactoring to be able to manage empty records
* TODO.org: handling an empty record
* lib/Biblio/Record/USBC.pm: removing a useless part of code
* lib/Biblio/Record/USBC.pm: correcting a bug (the code wasn't useless)
* t/00-first_design.t: present USBC is a string of 18 characters
* lib/Biblio/Record/USBC.pm: create a USBC without the check
* t/11-empty_record.t: correcting the check digit
* lib/Biblio/Record/USBC.pm: using Algorithm::LUHN to check the code
* t/00-first_design.t: removing the call to check_digit()
* t/09-check_digit.t: removing the call to check_digit()
* t/11-empty_record.t: removing the call to check_digit()
* TODO.org: empty record. Check