rustdoc: fixes
doc: slight design refresh
doc,rustdoc: store webfonts locally

- Avoids cross-domain requests restrictions
- Better availability of content
- No HTML queries needed for an offline build
rustdoc: bring it inline
auto merge of #13744 : adrientetar/rust/derp, r=brson

- Serve webfonts locally
- Style changes around `blockquote` and `code`
- Minor adjustments from previous changes

Bringing back updated examples: [modified tutorial](http://adrientetar.legtux.org/cached/rust-docs/tutorial.htm) and [modified manual](http://adrientetar.legtux.org/cached/rust-docs/manual.htm).
And for rustdoc, [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).