Extended Try RFC

[Rendered view.](https://github.com/TyOverby/rfcs/blob/extended_try/active/0000-extended-try.md)
Its also a good way to get some experience using this without affecting a really crucial macro. I mean that if we added this, decided it was a mistake, then took it out again, it could be painful. So there is a high bar for acceptance. If we had some use of this beforehand to convince us it was a good idea, then it would be easier to accept.

So, change the last sentence in my previous comment to "submit an RFC to merge the new macro in with Try!"