Make optional arguments last

[achingbrain]

Methods like the export from src/keys/rsa-class.js have optional arguments first in their signature. They should be last to follow conventions.

cc @dirkmc

[dirkmc]

I'd suggest we do this immediately after the async changes, and before we do a release, as it's a breaking change

[jacobheun]

I agree, since this needs to get pulled into several of the modules, we should make the change before going through that effort.

The only caveat is that it will make those migrations to async/await a little more confusing in PRs moving the params around.

[jacobheun]

async/await is in master, @achingbrain or @dirkmc, do either of you have time to do this? I'm working on a couple of other things but can take this after (likely tomorrow) if neither of you do.

[dirkmc]

Sure I can do it