doc/guide-ffi: A few minor typo/language fixes

Signed-off-by: Anton Lofgren <alofgren@op5.com>
Add example for str replace() and MaybeOwned

  - for 3 implementations of into_maybe_owned()
  - is_slice()
  - is_owned()
Guide: match
Guide: looping
Guide: Standard input
libstd: Add a few doc examples

This patch adds doc examples for the make_absolute, change_dir,
errors_string and args functions in the os module.
Stabilization for `owned` (now `boxed`) and `cell`

This PR is the outcome of the library stabilization meeting for the
`liballoc::owned` and `libcore::cell` modules.

Aside from the stability attributes, there are a few breaking changes:

* The `owned` modules is now named `boxed`, to better represent its
  contents. (`box` was unavailable, since it's a keyword.) This will
  help avoid the misconception that `Box` plays a special role wrt
  ownership.

* The `AnyOwnExt` extension trait is renamed to `BoxAny`, and its `move`
  method is renamed to `downcast`, in both cases to improve clarity.

* The recently-added `AnySendOwnExt` extension trait is removed; it was
  not being used and is unnecessary.

[breaking-change]
auto merge of #15591 : aturon/rust/box-cell-stability, r=alexcrichton

This PR is the outcome of the library stabilization meeting for the
`liballoc::owned` and `libcore::cell` modules.

Aside from the stability attributes, there are a few breaking changes:

* The `owned` modules is now named `boxed`, to better represent its
  contents. (`box` was unavailable, since it's a keyword.) This will
  help avoid the misconception that `Box` plays a special role wrt
  ownership.

* The `AnyOwnExt` extension trait is renamed to `BoxAny`, and its `move`
  method is renamed to `downcast`, in both cases to improve clarity.

* The recently-added `AnySendOwnExt` extension trait is removed; it was
  not being used and is unnecessary.

[breaking-change]
native: Search the child's PATH on win32

In order to have the spawning semantics be the same for unix/windows, the
child's PATH environment variable needs to be searched rather than the parent's
environment variable.

If the child is inheriting the parent's PATH, then no action need be taken as
windows will do the heavy lifting. If the child specifies its own PATH, then it
is searched beforehand for the target program and the result is favored if a hit
is found.

cc #15149, but does not close the issue because libgreen still needs to be
updated.
auto merge of #15158 : alexcrichton/rust/windows-paths, r=brson

In order to have the spawning semantics be the same for unix/windows, the
child's PATH environment variable needs to be searched rather than the parent's
environment variable.

If the child is inheriting the parent's PATH, then no action need be taken as
windows will do the heavy lifting. If the child specifies its own PATH, then it
is searched beforehand for the target program and the result is favored if a hit
is found.

cc #15149, but does not close the issue because libgreen still needs to be
updated.
std: make std::io::IoError{,Kind} implement Eq
auto merge of #15649 : catharsis/rust/rust-libstd-examples, r=alexcrichton

This patch adds doc examples for the make_absolute, change_dir,
errors_string and args functions in the os module.
auto merge of #15497 : jasonthompson/rust/docs/str3, r=cmr

  - for 3 implementations of into_maybe_owned()
  - is_slice()
  - is_owned()
auto merge of #15653 : erickt/rust/master, r=alexcrichton
glob::MatchOptions struct fields should be public
Document that Result.unwrap prints the Err's value

It is implied by the Show bound, but that implication can be missed.
auto merge of #15632 : masklinn/rust/patch-1, r=alexcrichton

I saw that it was bounded by `Show` but the implication is no guarantee (and had only 0.10 to test, where this behavior has been added to 0.11)
auto merge of #15655 : lightsofapollo/rust/glob-match-options-pub, r=alexcrichton

Not sure how to test this correctly I assume the current tests pass now because of the crate boundaries [and that this is fallout from private by default]?
doc: missing quote in keyword Send
auto merge of #15666 : yorkie/rust/patch-1, r=alexcrichton