Document for-loop in tutorial section on loops
 Explain container iteration in the loop tutorial

 As suggested by @pnkfelix in #12161, this extends the examples by a for-loop
 that iterates over a string as an example for container iteration.
Adds support for working with URL Paths

It is sometimes useful to parse just the path portion of a URL (path,
query string and fragment) rather than the entire URL.
mk: Clean up conditions for including dist.mk
mk: Add prepare.mk

This is a slightly more generic rewrite of install.mk. Currently
used for nothing, but we'll base all the binary distributables off it.
mk: Base the install target on prepare.mk
mk: Fix a dist bug

Fallout from moving doc/ to src/doc
mk: Base the windows dist target on prepare.mk
Remove Real trait and move methods into Float

This is part of the effort to simplify `std::num`, as tracked in issue #10387.
Minor documentation fixes in std::fmt

* Change '...your own time' => '...your own type'
* Fix typo in the Vector2D example
Clean up std::task docs, make TaskBuilder a real builder

Delete all the documentation from std::task that references linked
failure.

Tweak TaskBuilder to be more builder-like. .name() is now .named() and
.add_wrapper() is now .with_wrapper(). Remove .watched() and
.unwatched() as they didn't actually do anything.
Update clients of the TaskBuilder API
Address review feedback
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
Rename Bitwise::population_count to Bitwise::count_ones and add Bitwise::count_zeros

These are inspired by the [functions in the Julia standard library](http://docs.julialang.org/en/release-0.2/stdlib/base/#Base.count_ones).
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.
Forbid use of generics with foreign functions. Closes #10353.
Update tasks guide: SharedChan as been removed

The code examples are up to date, but the surrounding explanations are not.