string_to_proplist_property was being used with an or_return but
did not return an error. The function now returns an error when
it cannot identify a property.
This adds a program that will generate tables for use by the `core/unicode`
package. The table generated file will be `core/unicode/generated.odin`
It may be better to incorporate this into `generate_entity_table.odin`.
This can easily be accomplised if desired.
