Automsg

DO NOT MERGE

Not sure if barking up the wrong tree, but I'm fairly convinced that a very large number of the assert_one type issues we'll be generating are from `filter("").assert_one()`. Thinking about options including merging these and being able to know what the filter was (but not what it was on.)

`table.filter("LITERAL STRING").assert_one()` seems the most common type of thing to say. Maybe handling that as a special case?

Either way, I can now tell you to look in cells C4 and N7.

Not ready for primetime.