changes from 0.2 to 0.3
-----------------------

* add modules for the following number formats:
  - ISMN (International Standard Music Number)
  - ISAN (International Standard Audiovisual Number)
  - IMEI (International Mobile Equipment Identity)
  - MEID (Mobile Equipment Identifier)
  - GRid (Global Release Identifier)
* add modules for handling the following check digit algorithms:
  - the Verhoeff algorithm
  - the Luhn and Luhn mod N algorithms
  - some algorithms described in ISO/IEC 7064: Mod 11, 2, Mod 37, 2,
    Mod 97, 10, Mod 11, 10 and Mod 37, 36
* added more unit tests


changes from 0.1 to 0.2
-----------------------

* rename validate() function to is_valid() for all modules
* handle wrong types passed to is_valid() more gracefully
* add more tests and fix some minor bugs