RFC: new lifetime elision rules

[Rendered](https://github.com/aturon/rfcs/blob/lifetime-elision/active/0000-lifetime-elision.md)

Note: the core idea for this RFC and the initial survey both came from @wycats.
I find this rule a bit surprising (the others make perfect sense). I can intuitively see the motivation that self ought to be privileged but, I can't really justify why that is so. Looking at the examples below, the ones using this rule took me a lot longer to grok.