Extended Try RFC

[Rendered view.](https://github.com/TyOverby/rfcs/blob/extended_try/active/0000-extended-try.md)
I wanted this macro bad enough that I made my own cargo project that implements this RFC.
https://github.com/TyOverby/try_or

I'm pretty bad at writing macros, so I wouldn't suggest that this be made the official implementation, but I've found that it is *incredibly* handy.