Add rustup.sh to the repo

Just to have it somewhere to point to. Updating it will not
automatically update the one on static.rust-lang.org.
Changes a little the description of take in the guide

Closes #18218
Untabify rustup.sh
DSTify [T]/str extension traits

This PR changes the signature of several methods from `foo(self, ...)` to
`foo(&self, ...)`/`foo(&mut self, ...)`, but there is no breakage of the usage
of these methods due to the autoref nature of `method.call()`s. This PR also
removes the lifetime parameter from some traits (`Trait<'a>` -> `Trait`). These
changes break any use of the extension traits for generic programming, but
those traits are not meant to be used for generic programming in the first
place. In the whole rust distribution there was only one misuse of a extension
trait as a bound, which got corrected (the bound was unnecessary and got
removed) as part of this PR.

[breaking-change]
auto merge of #18273 : gamazeps/rust/issue18218, r=steveklabnik

Closes #18218
Long lines
auto merge of #17851 : brson/rust/rustup, r=alexcrichton

Just to have it somewhere to point to. Updating it will not
automatically update the one on static.rust-lang.org.
auto merge of #18291 : japaric/rust/dstify, r=aturon

This PR changes the signature of several methods from `foo(self, ...)` to `foo(&self, ...)`/`foo(&mut self, ...)`, but there is no breakage of the usage of these methods due to the autoref nature of `method.call()`s. This PR also removes the lifetime parameter from some traits (`Trait<'a>` -> `Trait`). These changes break any use of the extension traits for generic programming, but those traits are not meant to be used for generic programming in the first place. In the whole rust distribution there was only one misuse of a extension trait as a bound, which got corrected (the bound was unnecessary and got removed) as part of this PR.

I've kept the commits as small and self-contained as possible for reviewing sake, but I can squash them when the review is over.

See this [table] to get an idea of what's left to be done. I've already DSTified [`Show`][show] and I'm working on `Hash`, but bootstrapping those changes seem to require a more recent snapshot (#18259 does the trick)

r? @aturon 
cc #16918 

[show]: https://github.com/japaric/rust/commits/show
[table]: https://docs.google.com/spreadsheets/d/1MZ_iSNuzsoqeS-mtLXnj9m0hBYaH5jI8k9G_Ud8FT5g/edit?usp=sharing
Rename fail! to panic!

https://github.com/rust-lang/rfcs/pull/221

The current terminology of "task failure" often causes problems when
writing or speaking about code. You often want to talk about the
possibility of an operation that returns a Result "failing", but cannot
because of the ambiguity with task failure. Instead, you have to speak
of "the failing case" or "when the operation does not succeed" or other
circumlocutions.

Likewise, we use a "Failure" header in rustdoc to describe when
operations may fail the task, but it would often be helpful to separate
out a section describing the "Err-producing" case.

We have been steadily moving away from task failure and toward Result as
an error-handling mechanism, so we should optimize our terminology
accordingly: Result-producing functions should be easy to describe.

To update your code, rename any call to `fail!` to `panic!` instead.
Assuming you have not created your own macro named `panic!`, this
will work on UNIX based systems:

    grep -lZR 'fail!' . | xargs -0 -l sed -i -e 's/fail!/panic!/g'

You can of course also do this by hand.

[breaking-change]
Update infrastructure for fail -> panic

This includes updating the language items and marking what needs to
change after a snapshot.

If you do not use the standard library, the language items you need to
implement have changed. For example:

```rust
 #[lang = "fail_fmt"] fn fail_fmt() -> ! { loop {} }
```

is now

```rust
 #[lang = "panic_fmt"] fn panic_fmt() -> ! { loop {} }
```

Related, lesser-implemented language items `fail` and
`fail_bounds_check` have become `panic` and `panic_bounds_check`, as
well. These are implemented by `libcore`, so it is unlikely (though
possible!) that these two renamings will affect you.

[breaking-change]