Make SynonymFilterFactory more extendable

As is, reading rules from the ResourceLoader is baked into inform(ResourceLoader loader). It would be nice to be able to load custom rules w/o needing to rewrite the whole thing. This issue changes two things:

1. Changes List<String> to Iterable<String> because we don't really need a list
2. adds protected Iterable<String> loadRules( String synonyms, ResourceLoader loader ) – so subclasses could fill their own