Support for incremental extractions (only load records new since last run)

[hyfen]

If using Chronicle-ETL to do incremental backups of personal data or syncing to other services, it's annoying to extract a full set of records each time a job is run. An incremental extraction system could let users extract records created/modified since the last time the job was run.

The guts of it (some already half-implemented):

• a system for persisting results from a job (a row saved in a sqlite db stored in $XDG_DATA_HOME)
• a way to specify that a job should continue from the last run
• setting the since option on a job automatically based on results of the last run

This system won't work with ad-hoc jobs specified with only CLI flags. It would require either a stable name for a job or a config file (perhaps this is one and the same?)