Add RFC for assign param syntax.

[jemc]

This PR adds my RFC for assign param syntax.

Note: This RFC is based on this other RFC and assumes the other one will be accepted when presenting its syntax examples

[aturley]

Discuss more next week.

[SeanTAllen]

@jemc how would you feel about moving forward with this. instead of @? I'd like to move this and #173 forward but we have some syntax issues to resolve. I'm in favor of "this" because it is the least breaking option.

[jemc]

I'd agree that this. is "better than nothing" for the purposes of this RFC, so I'd be good with amending this RFC to use that syntax. It's still less boilerplate than the current status quo.

For #173 I would not be in favor of making that change with this. - I think it's too much friction added for something so ubiquitous.

[SeanTAllen]

We appear to have an impasse on #173, but it would be good to move forward with this RFC so let's do that and continue to discuss #173.

[jasoncarr0]

One more note possibly worth adding: are any names supported for keyword argument syntax? Does that create semver issues with the name requirements?

[SeanTAllen]

It was noted on the sync call that @jemc will note that how this interacts with named arguments in unresolved questions.

[SeanTAllen]

This was accepted during sync. I will do the merge and what not later.