RFC: Finalizing more naming conventions

This conventions RFC tweaks and finalizes a few long-running de facto
conventions, including capitalization/underscores, and the role of the `unwrap` method.

See [this RFC](https://github.com/rust-lang/rfcs/pull/328) for a competing proposal for `unwrap`.

[Rendered](https://github.com/aturon/rfcs/blob/finalizing-naming-conventions/text/0000-finalizing-naming-conventions.md)
I personally prefer `crate-name` and then importing as a shorter name for crates that *must* be multiple words, though single words is strongly preferable. I think this works because they will usually be imported as a single word, i.e. `extern crate "replace-map" as rmap; // from iron` which is much nicer at the usage site than something like `raw_trait_object::vtable(..)`.