libstd: improve os::args() doc
Guide: add a pointer to play.rust-lang.org and explain how to run the code examples.
Reference: Add missing third dot of range
librustrt: check for mips+linux config in stack_overflow
New guide: error handling
Register new snapshots
Feature gate non-ASCII lifetime identifiers

Fixes #19069.
deriving: error out when used on a non-type

Besides being more helpful, this gives us the flexibility to later define
a meaning for something like

    #[deriving(...)]
    mod bar { ... }
Error handling guide
Switch to an independent enum for `Lit*` subtokens.
Update src/grammar for language changes.
Update makefiles to ensure src/grammar/verify.rs is built.

It's not run, but this ensures that the code at least doesn't go out of
date.
rustc: avoid `use`-ing `syntax::ast::*`.
rustc: middle: rename `ty::t` to `Ty` and use it unqualified everywhere.
rustc: middle: ty: replace unsafe pointers with references in Ty.
rustc: fix fallout of adding the `'tcx` lifetime to `Ty`.
rustc: fix fallout of making `Ty` an alias for `&TyS` instead of a wrapper.
rustc: middle: avoid clones in ty_fn_{sig,args}.
rustc: middle: remove obsolete ty::get.
rustc: middle: simplify primitive type declaration in ty.