add "(see below)" to a reference to a new concept

This is because I observed someone reading the tutorial who thought they'd
missed something when they got to the mention of variable bindings.

This patch doesn't reflow the paragraphs so that you can see the semantic
change that I made, and a subsequent patch will reflow this paragraph.

Fixes https://github.com/rust-lang/rust/issues/13570.
reflow with emacs fill-paragraph (fill-column 71)
Guide: install instructions
fix feedback from @huonw
thanks @sfackler
Guide: Hello, world!

Let's write our first Rust program!
Register new snapshots

This change starts denying `*T` in the parser. All code using `*T` should ensure
that the FFI call does indeed take `const T*` on the other side before renaming
the type to `*const T`.

Otherwise, all code can rename `*T` to `*const T`.

[breaking-change]
Add extra ignore directives.
json: Fix handling of NaN/Infinity

The JSON spec requires that these special values be serialized as null; the current serialization breaks any conformant JSON parser. So encoding needs to output "null",  to_json on floating-point types can return Null as well as Number, and reading null when specifically expecting a number should be interpreted as NaN. There's no way to round-trip Infinity.
auto merge of #15162 : steveklabnik/rust/install_instructions, r=brson

This has my voice *very strongly*. I'm not sure if it's too much. I'd find it okay if I had to tone it back, and I don't want it to be _too strong_, but clinical docs are boring.
Remove unnecessary to_string calls

This commit removes superfluous to_string calls from various places
auto merge of #15181 : steveklabnik/rust/hello_world, r=brson

This is built on top of https://github.com/rust-lang/rust/pull/15162 . https://github.com/steveklabnik/rust/commit/cccae83d922f5aade2b7cca96579521cc35ced59 is the only new commit, you may want to look at that rather than the whole diff.

Writing our first Rust program together. This is the most crucial step, so I go to a fairly deep level of detail. Future sections will move more quickly.
Fix a typo and a small syntactic error.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
auto merge of #15194 : Sawyer47/rust/to-string-cleanup, r=alexcrichton

This commit removes superfluous to_string calls from various places
auto merge of #15192 : mrec/rust/json-nan, r=alexcrichton

The JSON spec requires that these special values be serialized as "null"; the current serialization breaks any conformant JSON parser. So encoding needs to output "null",  `to_json` on floating-point types can return `Null` as well as `Number` values, and reading a `Null` value when specifically expecting a number should be interpreted as NaN. There's no way to round-trip Infinity through JSON.

This is my first attempt at both writing Rust and opening pull requests, so please dial your derp detector up to eleven when reviewing. A `rustc --test lib.rs` in `libserialize` passes all tests; a `make check` of the whole tree fails with the error below, but it doesn't look obviously related and the docs say that `make check` is known to be flaky on Windows.

    ---- [compile-fail] compile-fail/svh-change-significant-cfg.rs stdout ----
            task '[compile-fail] compile-fail/svh-change-significant-cfg.rs' failed at 'called `Result::
    unwrap()` on an `Err` value: couldn't create file (end of file (unknown error); path=i686-pc-mingw32
    \test\compile-fail\svh-a-base.err; mode=truncate; access=write)', C:\msys\home\Mike\rust\src\libcore
    \result.rs:545

Incidentally, it may just be my lack of familiarity with the language and its idioms, but the duplication between `Encoder`/`PrettyEncoder` had a distinct code smell to it. The size of the file (~3500 lines) also made it a bit hard to navigate. Has there been any discussion of refactoring and/or breaking it up? I couldn't find anything in Issues except the ancient #9028.
auto merge of #15197 : omasanori/rust/doc-fix, r=alexcrichton
Guide: Hello, cargo
Add a note that this requires `git`.
Fix capitalization of Issue.

@chris-morgan and @huonw pointed out that even though the feature
is a proper noun, we're using it in a more generic sense here.
tha -> than

Thanks @huonw :heart: