Got rid of warnings issued by 3.3

"failUnless" and "assert_"  ==> assertTrue and assertFalse
Migrated ctypes xmp_copy and xmp_get_property calls into exempi module.  #issue2
Fixed get_property docstring for sphinx build.
Moved xmp_copy, xmp_parse, xmp_get_property support from types module to exempi.  #issue2
parse_from_str method uses exempi module, no longer returns a bool.  #issue2
Moved exempi iterator base functionality into exempi module.
Refactored several methods to use ctypes exempi module.

Exempi library routines include xmp_new_empty, xmp_free,
xmp_get_property_float, xmp_get_property_bool, xmp_get_property_int32,
xmp_get_property_int64, xmp_get_array_item, xmp_set_property,
xmp_set_array_item, xmp_append_array_item, xmp_get_localized_text.  #issue2
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
Always convert xmp_string_cstr results to utf-8.  #issue2
Added a latin-1 test.
Added test where encoding needs 3 bytes per codepoint.
Added negative test for bad schema.  Must revisit.
Refactored xmp_iterator_skip to use exempi module.  #issue2
Refactored datetime routines, added timezone support.
Some formatting.
Progress.
Added test_does_array_item_exist to verify fix.  #3

Also added test_exempi_core for code coverage purposes.
Rewrote does_array_item_exist method.  Closes #3