Added support for varint structure members.

[cmebarrow]

Arrays are now implemented, accessed using ArrayFW and ArrayFW. Example mutation:

flyweightRW.varint32Array(a -> a.item(b -> b.set(-1))
                                .item(b -> b.set(1)))

Example accessor:

flyweightRO.varint32Array().forEach(v -> myIntegerList.add(v.value()));