Consider renaming `wac encode` to `wac compose`

[rylev]

The phrasing "encoding a composition" makes a ton of sense once you've got a solid understanding of what wac is doing under the hood, but arguably does not capture the most interesting bit of what wac encode is actually doing. I suppose wac encode has the advantage of having symmetry with a future wac decode, but wac compose IMO captures the main thrust of the command's purpose and makes it extremely clear what is happening.