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/liblog/lib.rs

@@ -239,21 +239,15 @@ struct DefaultLogger {
 }
 
 /// Wraps the log level with fmt implementations.
-#[derive(Copy, PartialEq, PartialOrd)]
+#[derive(Copy, PartialEq, PartialOrd, Show)]
 pub struct LogLevel(pub u32);
 
-impl fmt::Show for LogLevel {
-    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        fmt::String::fmt(self, fmt)
-    }
-}
-
-impl fmt::String for LogLevel {
+impl fmt::Display for LogLevel {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         let LogLevel(level) = *self;
         match LOG_LEVEL_NAMES.get(level as uint - 1) {
-            Some(ref name) => fmt::String::fmt(name, fmt),
-            None => fmt::String::fmt(&level, fmt)
+            Some(ref name) => fmt::Display::fmt(name, fmt),
+            None => fmt::Display::fmt(&level, fmt)
         }
     }
 }