Fix error in reStructuredText source.
Refactor to avoid an unreachable!().
Minor tweak in the fmt_header return type change.

(That is, where before it returned `fmt::Result` and now it returns
`IoResult`, which *does* implement `Show`.)
gitignore doc/implementors/
Rust update: collections::hashmap moved into std.
Upstream Rust changes.
Yay! Byte/s literals!