Added some named initialization parms in __init__() to control
the following :
  min_age and max_age controls the age range that is selected
  zip_type is either 5 (only 5-digit zips),
    9 (only 9 digit zips) or None (the default, which is random)

Also added tests for these in test_api.py

Fixed problem in python26 of using sys.version_info.major to determine
the version type of the python interpreter (the "named" tuple is not
supported prior to python27) so instead we use sys.version_info[0]