This release changes the serialization interface going from a generic "serialize(...)" naming to a more explicit naming. Now matador will have

• "on_primary_key(...)"
• "on_attribute(...)"
• "on_belongs_to(...)"
• "on_has_one(...)"
• "on_has_many(...)"
  for the serialization interface. This leads to a more readable database entity description and the remove of the "identifier", "has_one" and "belongs_to" classes. For primary key the plain datatype (integral and sized string -> varchar) can be used. For foreign object only "object_ptr" is used.

Furthermore the interface is extended with a "field_attribute" parameter. This class contains constraints like NOT_NULL, PRIMARY_KEY or UNIQUE and a size parameter used for varchar (through std::string)