auto merge of #13587 : adrientetar/rust/more-docs, r=brson

- Use Fira Sans for headlines, Heuristica for the body (Adobe Utopia derivative). Both are licensed under the SIL OFL license. (I didn't include BoldItalic because it is sparingly used.)
- Split TOC into 2 columns for the docs except manual (too tall, too wide to be readable).
- Some fixes to rustdoc, bring styles in coherency with eachother
- A few tweaks

Two examples: [modified tutorial](http://adrientetar.legtux.org/cached/rust-docs/tutorial.htm) and [modified manual](http://adrientetar.legtux.org/cached/rust-docs/manual.htm).

Rustdoc got some fixes, here is [modified `enum.FileType`](http://adrientetar.legtux.org/cached/rust-docs/enum.FileType.htm), [modified `std`](http://adrientetar.legtux.org/cached/rust-docs/std.htm) and [modified `std::io`](http://adrientetar.legtux.org/cached/rust-docs/io.htm).

#13484, #13485 follow-up.

cc @brson

src/librustdoc/html/render.rs

@@ -975,7 +975,7 @@ impl<'a> fmt::Show for Item<'a> {
                 format!("{}-{}", self.item.source.loline, self.item.source.hiline)
             };
             try!(write!(fmt.buf,
-                          "<a class='source'\
+                          "<a class='source' \
                               href='{root}src/{krate}/{path}.html\\#{href}'>\
                               [src]</a>",
                           root = self.cx.root_path,