Consider adding buffered async output, maybe DETS + gen_stage

[mhsdef]

Right now the async casting logic heavily assumes short WP.com API outages. Historically, that's fair, but I think we can do better.

It'd also be nice to be more robust against proc brutal kills or unexpected host shutdowns.

[mhsdef]

Ripped that "cast" nonsense out.

What I am trying to talk about here is buffered output. The use case is a service that's quite reliant on persisting off to WP.com...and gets interrupted.