Read support for store modules to allow checking against previous commits #6
Description
In order to compare against previous commit-attached records (eg: see #1), we'll want some way of getting at previous data. Easy start for that would be to support a read-mode for "output" modules. Consider calling these "persistence" modules, or something?
Databases are an easy shout - if we're writing, reading isn't crazy, but there'll be some that support will be awkward or limited. Consider a CSV-append output module (#5) - file-scans will be slow and cumbersome. Not the end of the world, but we'll want to account for that in any spec. Also consider truly write-only options (eg: an HTTPS POST webhook module?) - they'll presumably just block things out.
...though we could totally do a GET -> JSON array option for that...