Remove Real trait and move methods into Float

This is part of the effort to simplify `std::num`, as tracked in issue #10387.
Implement Unix domain sockets in libnative
Move unix pipes implementation to pipe_unix.rs

The windows named pipes implementation will have almost nothing to do with unix
pipes, so I think it's best if they live in separate files.
Implement named pipes for windows, touch up unix

* Implementation of pipe_win32 filled out for libnative
* Reorganize pipes to be clone-able
* Fix a few file descriptor leaks on error
* Factor out some common code into shared functions
* Make use of the if_ok!() macro for less indentation

Closes #11201
Remove Freeze bounds from sync::MutexArc

With Rc no longer trying to statically prevent cycles (and thus no
longer using the Freeze bound), it seems appropriate to remove that
restriction from MutexArc as well.
Update tasks guide: SharedChan as been removed

The code examples are up to date, but the surrounding explanations are not.
Added more scripts to tidy check
Remove the compile-fail test that's now obsolete
backticks for syntax elements
Spellcheck library docs.
Fix a segfault in the rustuv tests

The details can be found in the comments I added to the test, but the gist of it
is that capturing output injects rescheduling a green task on failure, which
wasn't desired for the test in question.

cc #12340
auto merge of #12243 : dguenther/rust/extend-tidy, r=alexcrichton

Extends the license and formatting check to `*.js` files in `src/doc` and `*.sh`, `*.pl`, `*.c`, and `*.h` files in `src/etc`. As best as I could tell, these files should be covered under the Rust project license.

cc @brson: Do any other scripts need a license? I'd like to double-check that this PR closes #4534.
Test ordering of glue_drop and glue_takew in self-re-assignment. Closes #3290.
Made fail_bounds_check more careful with strings.

Fixes GH #11976.
auto merge of #12103 : alexcrichton/rust/unix, r=brson

There's a few parts to this PR

* Implement unix pipes in libnative for unix platforms (thanks @Geal!)
* Implement named pipes in libnative for windows (terrible, terrible code)
* Remove `#[cfg(unix)]` from `mod unix` in `std::io::net`. This is a terrible name for what it is, but that's the topic of #12093.

The windows implementation was significantly more complicated than I thought it would be, but it seems to be passing all the tests. now.

Closes #11201
auto merge of #12321 : bjz/rust/remove-real, r=alexcrichton

This is part of the effort to simplify `std::num`, as tracked in issue #10387. It is also a step towards a proper IEEE-754 trait (see #12281).
auto merge of #12342 : ehsanul/rust/remove-shared-chan-tasks-guide, r=alexcrichton

The code examples are up to date, but the surrounding explanations are not.
auto merge of #12345 : huonw/rust/speeling, r=cmr
std::str: safen and optimize is_utf8.

This uses a vector iterator to avoid the necessity for unsafe indexing,
and makes this function slightly faster. Unfortunately #11751 means that
the iterator comes with repeated `null` checks which means the
pure-ASCII case still has room for significant improvement (and the
other cases too, but it's most significant for just ASCII).

Before:

    is_utf8_100_ascii             ... bench:       143 ns/iter (+/- 6)
    is_utf8_100_multibyte         ... bench:       134 ns/iter (+/- 4)

After:

    is_utf8_100_ascii             ... bench:       123 ns/iter (+/- 4)
    is_utf8_100_multibyte         ... bench:       115 ns/iter (+/- 5)
std: convert first_non_utf8_byte to use the iterator.

This makes it very slightly faster, especially when the string is valid
UTF-8, and completely removes the use of `unsafe` from the first half.

Before:

    from_utf8_lossy_100_ascii              ... bench:       151 ns/iter (+/- 17)
    from_utf8_lossy_100_invalid            ... bench:       447 ns/iter (+/- 33)
    from_utf8_lossy_100_multibyte          ... bench:       135 ns/iter (+/- 4)
    from_utf8_lossy_invalid                ... bench:       124 ns/iter (+/- 10

After:

    from_utf8_lossy_100_ascii              ... bench:       119 ns/iter (+/- 8)
    from_utf8_lossy_100_invalid            ... bench:       454 ns/iter (+/- 16)
    from_utf8_lossy_100_multibyte          ... bench:       116 ns/iter (+/- 9)
    from_utf8_lossy_invalid                ... bench:       119 ns/iter (+/- 9)