shortened name of "Metabolite" to "Mtab"
shortened name of "experiment" to "exp_name", will need proper
foreign key refs
added Exp class, starting to wire in it. checkpointing
adding metadata support. etl appears to work, doesn't break earlier queries,
checkpointing while I test
etl now works with full information model. could improve with association proxies.
etl is now pretty darned slow on SQLite, but queries are pretty reasonable.