RFC: Resolve numerous naming conventions

This is a conventions RFC for settling a number of remaining naming conventions:

* Referring to types in method names
* Iterator type names
* Additional iterator method names
* Getter/setter APIs
* Associated types
* Trait naming
* Lint naming
* Suffix ordering
* Prelude traits

It also proposes to standardize on lower case error messages within the compiler
and standard library.

[Rendered](https://github.com/aturon/rfcs/blob/conventions-galore/active/0000-conventions-galore.md)


What about `[T, ..N]`? `array`? `fixed`? In cgmath [we use `fixed`](https://github.com/bjz/cgmath-rs/blob/master/src/array.rs#L91-L100).