Metric Persistance #514
Description
It'd be neat to be able to have the option to persist the metric state to disk and be able to restore from it on startup, in the event a rust binary is restarted (catching ctrl-c/sigint) or crashes (custom panic hook). Storing the text encoding to disk can work, but there needs to be a way to decode and restore data from the text file. An incremental db approach could also work but I think it'd need more plumbing to be able to hook into when metrics are updated.