Payload as BLOB

[edsu]

I wonder if we should use BLOB columns for the payload instead of str? Now that we have a way to migrate the schema it should be pretty simple?

I'm not sure it makes a ton of difference for SQLite but it might be a bit more descriptive of what that column can contain. I think some datasette plugins like datasette-render-images will key off the BLOB column type to try to render the content.