it should be possible to change default splitting rules

for example, as discussed at https://irclogs.baserock.org/%23baserock.2016-09-12.log.html#t2016-09-12T17:33:15

it seems the best way to address this is to leave all splitting to the higher-level assembly logic (strata, system). so that will mean an artifact-version bump, since chunk metafiles shouldn't contain any splitting information