std: Rename Show/String to Debug/Display

This commit is an implementation of [RFC 565][rfc] which is a stabilization of
the `std::fmt` module and the implementations of various formatting traits.
Specifically, the following changes were performed:

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0565-show-string-guidelines.md

* The `Show` trait is now deprecated, it was renamed to `Debug`
* The `String` trait is now deprecated, it was renamed to `Display`
* Many `Debug` and `Display` implementations were audited in accordance with the
  RFC and audited implementations now have the `#[stable]` attribute
  * Integers and floats no longer print a suffix
  * Smart pointers no longer print details that they are a smart pointer
  * Paths with `Debug` are now quoted and escape characters
* The `unwrap` methods on `Result` now require `Display` instead of `Debug`
* The `Error` trait no longer has a `detail` method and now requires that
  `Display` must be implemented. With the loss of `String`, this has moved into
  libcore.
* `impl<E: Error> FromError<E> for Box<Error>` now exists
* `derive(Show)` has been renamed to `derive(Debug)`. This is not currently
  warned about due to warnings being emitted on stage1+

While backwards compatibility is attempted to be maintained with a blanket
implementation of `Display` for the old `String` trait (and the same for
`Show`/`Debug`) this is still a breaking change due to primitives no longer
implementing `String` as well as modifications such as `unwrap` and the `Error`
trait. Most code is fairly straightforward to update with a rename or tweaks of
method calls.

[breaking-change]
Closes #21436

src/test/compile-fail/dst-index.rs

@@ -12,7 +12,7 @@
 // can't be used as rvalues
 
 use std::ops::Index;
-use std::fmt::Show;
+use std::fmt::Debug;
 
 struct S;
 
@@ -31,9 +31,9 @@ struct T;
 impl Copy for T {}
 
 impl Index<usize> for T {
-    type Output = Show + 'static;
+    type Output = Debug + 'static;
 
-    fn index<'a>(&'a self, idx: &usize) -> &'a (Show + 'static) {
+    fn index<'a>(&'a self, idx: &usize) -> &'a (Debug + 'static) {
         static x: usize = 42;
         &x
     }

src/test/compile-fail/issue-14853.rs

@@ -8,12 +8,12 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use std::fmt::Show;
+use std::fmt::Debug;
 
 trait Str {}
 
 trait Something {
-    fn yay<T: Show>(_: Option<Self>, thing: &[T]);
+    fn yay<T: Debug>(_: Option<Self>, thing: &[T]);
 }
 
 struct X { data: u32 }

src/test/compile-fail/issue-15094.rs

@@ -12,19 +12,19 @@
 
 use std::{fmt, ops};
 
-struct Shower<T> {
+struct Debuger<T> {
     x: T
 }
 
-impl<T: fmt::Show> ops::Fn<(), ()> for Shower<T> {
+impl<T: fmt::Debug> ops::Fn<(), ()> for Debuger<T> {
     fn call(&self, _args: ()) {
 //~^ ERROR `call` has an incompatible type for trait: expected "rust-call" fn, found "Rust" fn
         println!("{:?}", self.x);
     }
 }
 
-fn make_shower<T>(x: T) -> Shower<T> {
-    Shower { x: x }
+fn make_shower<T>(x: T) -> Debuger<T> {
+    Debuger { x: x }
 }
 
 pub fn main() {

src/test/compile-fail/liveness-use-after-send.rs

@@ -8,13 +8,13 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-fn send<T:Send + std::fmt::Show>(ch: _chan<T>, data: T) {
+fn send<T:Send + std::fmt::Debug>(ch: _chan<T>, data: T) {
     println!("{:?}", ch);
     println!("{:?}", data);
     panic!();
 }
 
-#[derive(Show)]
+#[derive(Debug)]
 struct _chan<T>(isize);
 
 // Tests that "log(debug, message);" is flagged as using