etc: Add box as a keyword to editor configs

This keyword is about to be used much more often than it was a few weeks ago,
it's time to tell editors about the new keyword.
std: Modernize the local_data api

This commit brings the local_data api up to modern rust standards with a few key
improvements:

* The `pop` and `set` methods have been combined into one method, `replace`

* The `get_mut` method has been removed. All interior mutability should be done
  through `RefCell`.

* All functionality is now exposed as a method on the keys themselves. Instead
  of importing std::local_data, you now use "key.replace()" and "key.get()".

* All closures have been removed in favor of RAII functionality. This means that
  get() and get_mut() no long require closures, but rather return
  Option<SmartPointer> where the smart pointer takes care of relinquishing the
  borrow and also implements the necessary Deref traits

* The modify() function was removed to cut the local_data interface down to its
  bare essentials (similarly to how RefCell removed set/get).

[breaking-change]
auto merge of #13835 : alexcrichton/rust/localdata, r=brson

This commit brings the local_data api up to modern rust standards with a few key
improvements:

* All functionality is now exposed as a method on the keys themselves. Instead
  of importing std::local_data, you now use "key.set()" and "key.get()".

* All closures have been removed in favor of RAII functionality. This means that
  get() and get_mut() no long require closures, but rather return
  Option<SmartPointer> where the smart pointer takes care of relinquishing the
  borrow and also implements the necessary Deref traits

* The modify() function was removed to cut the local_data interface down to its
  bare essentials (similarly to how RefCell removed set/get).

[breaking-change]
auto merge of #13986 : alexcrichton/rust/box-keyword, r=thestinger

This keyword is about to be used much more often than it was a few weeks ago,
it's time to tell editors about the new keyword.
Add compiler flag to force color output

This adds the flag --force-color-output. Why this is beneficial is
explained in issue #12881.

Please note that this commit doesn't include any regression tests. I
thought about how I'd write a test for this and it doesn't seem to be
worth the effort to me for a UI change like this.

Fixes #12881.