Add myself to AUTHORS.
Recorded 3.3 support.
Refactored some ctypes entry points into exempi module.

Exempi library routines include xmp_set_property_float, xmp_set_property_bool,
xmp_set_property_int32, xmp_set_property_int64, xmp_delete_property,
xmp_has_property, xmp_set_localized_text.  #issue2