Feat/multitag (Issue #41: Support for text information frames with multiple strings in ID3v2.4)

I settled on returning `List` from the getters, and taking `Iterable` in the setters. I also took the liberty of changing the signatures on `get/setChapters` and `get/setChapterTOC` to match (the List interface is close enough to ArrayList that this hopefully won't break any existing code).

Note that the plural getters return fixed-size lists (native arrays wrapped via `Arrays.asList`) to avoid unnecessary copying. This should probably be documented, but I'm not sure where.