This breaks a fair amount of code. The typical patterns are:

* `for _ in range(0, 10)`: change to `for _ in range(0u, 10)`;

* `println!("{}", 3)`: change to `println!("{}", 3i)`;

* `[1, 2, 3].len()`: change to `[1i, 2, 3].len()`.

RFC #30. Closes #6023.

[breaking-change]

Closes #14996

* The select/plural methods from format strings are removed
* The # character no longer needs to be escaped
* The \-based escapes have been removed
* '{{' is now an escape for '{'
* '}}' is now an escape for '}'

Closes #14810
[breaking-change]

Now that rustdoc understands proper language tags
as the code not being Rust, we can tag everything
properly.

This change tags examples in other languages by
their language. Plain notations are marked as `text`.
Console examples are marked as `console`.

Also fix markdown.rs to not highlight non-rust code.

This was only ever a transitionary macro.

This commit moves reflection (as well as the {:?} format modifier) to a new
libdebug crate, all of which is marked experimental.

This is a breaking change because it now requires the debug crate to be
explicitly linked if the :? format qualifier is used. This means that any code
using this feature will have to add `extern crate debug;` to the top of the
crate. Any code relying on reflection will also need to do this.

Closes #12019

[breaking-change]

[breaking-change]

[breaking-change]

In an attempt to phase out the std::num::strconv module's string formatting
functionality, this commit reimplements some provided methods for formatting
integers on top of format!() instead of the custom (and slower) implementation
inside of num::strconv.

Primarily, this deprecates int_to_str_bytes_common

1. Wherever the `buf` field of a `Formatter` was used, the `Formatter` is used
   instead.
2. The usage of `write_fmt` is minimized as much as possible, the `write!` macro
   is preferred wherever possible.
3. Usage of `fmt::write` is minimized, favoring the `write!` macro instead.

This commit moves all possible functionality from the standard library's string
formatting utilities into the core library. This is a breaking change, due to a
few tweaks in the semantics of formatting:

1. In order to break the dependency on the std::io module, a new trait,
   FormatWriter was introduced in core::fmt. This is the trait which is used
   (instead of Writer) to format data into a stream.
2. The new FormatWriter trait has one method, write(), which takes some bytes
   and can return an error, but the error contains very little information. The
   intent for this trait is for an adaptor writer to be used around the standard
   library's Writer trait.
3. The fmt::write{,ln,_unsafe} methods no longer take &mut io::Writer, but
   rather &mut FormatWriter. Since this trait is less common, all functions were
   removed except fmt::write, and it is not intended to be invoked directly.

The main API-breaking change here is that the fmt::Formatter structure will no
longer expose its `buf` field. All previous code writing directly to `f.buf`
using writer methods or the `write!` macro will now instead use `f` directly.

The Formatter object itself implements the `Writer` trait itself for
convenience, although it does not implement the `FormatWriter` trait. The
fallout of these changes will be in the following commits.

[breaking-change]