Poll command to update existing feeds

[eyeseast]

Grabbing something @simonw said on Slack:

I like the idea of a feeds table - for a couple of reasons beyond just having something to foreign key against
You could stash information about when each feed was last polled - maybe even store an ETag for more efficient polling against sites that support that
And... that way you could have a feeds-to-sqlite poll feeds.db command which you run on cron which then runs a new fetch for every feed in that table
Which you could accompany with a feeds-to-sqlite feeds.db https://.../feed.xml which adds a new URL to that table - and now you've implemented a full feed reader :)

So maybe write this poll command. It's a good idea.