Configuration for where outputs should be documented

[a-frantz]

Continuation/migration of https://github.com/stjude-rust-labs/sprocket/issues/3

The gist: The community is divided here. Some of us are of the opinion that outputs should be documented in the meta section and some of us feel they should be documented in the parameter_meta section. IMO we need to support both. What exactly that looks like is a bit in the air.

In the absence of any public outrage, this repo is going to take the stance that the default behavior should be output documentation belongs in the meta section. But we should provide some simple and straightforward way to change that behavior so that output docs will be looked for in the parmater_meta section.