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It's not run, but this ensures that the code at least doesn't go out of
date.
libs: stabilize most numerics after RFC changes

This commit adds stability markers for the APIs that have recently been
aligned with [numerics
reform](https://github.com/rust-lang/rfcs/pull/369). For APIs that were
changed as part of that reform, `#[unstable]` is used to reflect the
recency, but the APIs will become `#[stable]` in a follow-up pass.

In addition, a few aspects of the APIs not explicitly covered by the RFC
are marked here -- in particular, constants for floats.

This commit does not mark the `uint` or `int` modules as `#[stable]`,
given the ongoing debate out the names and roles of these types.

Due to some deprecation (see the RFC for details), this is a:

[breaking-change]
Fallout from deprecation
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}.