Should the single ci command alias be split into multiple workflow steps?

[armanbilge]

Spinning out of http4s/sbt-http4s-org#120 (comment).

This is a pattern I adopted from sbt-spiewak, but it obviously has tradeoffs.

Pros:

• a single command, that in theory you can run locally to emulate CI
• works well when split into ciJVM, ciJS, etc.
• doesn't have to restart sbt for each step

Cons:

• harder to see on what step a build fails
• difficult to progressively build up the commands in the alias, or remove stuff
• sometimes, restarting sbt is actually a good thing

[armanbilge]

I think fixing #61 would make it feasible to split CI into separate steps while being friendly to platform-crossed-matrices.