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

Signed-off-by: Anton Lofgren <alofgren@op5.com>
Guide: looping
Guide: Standard input
Convert a first batch of diagnostics to have error codes
add UnicodeStrSlice width() function
add Graphemes iterator; tidy unicode exports

- Graphemes and GraphemeIndices structs implement iterators over
  grapheme clusters analogous to the Chars and CharOffsets for chars in
  a string. Iterator and DoubleEndedIterator are available for both.

- tidied up the exports for libunicode. crate root exports are now moved
  into more appropriate module locations:
  - UnicodeStrSlice, Words, Graphemes, GraphemeIndices are in str module
  - UnicodeChar exported from char instead of crate root
  - canonical_combining_class is exported from str rather than crate root

Since libunicode's exports have changed, programs that previously relied
on the old export locations will need to change their `use` statements
to reflect the new ones. See above for more information on where the new
exports live.

closes #7043
[breaking-change]
auto merge of #15531 : steveklabnik/rust/guide_looping, r=brson
auto merge of #15534 : steveklabnik/rust/guide_stdin, r=brson
Extend --pretty flowgraph=ID to include dataflow results in output.

Use one or more of the following `-Z` flag options to tell the
graphviz renderer to include the corresponding dataflow sets (after
the iterative constraint propagation reaches a fixed-point solution):

  * `-Z flowgraph-print-loans` : loans computed via middle::borrowck
  * `-Z flowgraph-print-moves` : moves computed via middle::borrowck::move_data
  * `-Z flowgraph-print-assigns` : assignments, via middle::borrowck::move_data
  * `-Z flowgraph-print-all` : all of the available sets are included.

Fix #15016.

----

This also adds a module, `syntax::ast_map::blocks`, that captures a
common abstraction shared amongst code blocks and procedure-like
things.  As part of this, moved `ast_map.rs` to subdir
`ast_map/mod.rs`, to follow our directory layout conventions.

(incorporated review feedback from huon, acrichto.)
auto merge of #15371 : pnkfelix/rust/fsk-render-dataflow-on-dot, r=alexcrichton

Use one or more of the following `-Z` flag options to tell the
graphviz renderer to include the corresponding dataflow sets (after
the iterative constraint propagation reaches a fixed-point solution):

  * `-Z flowgraph-print-loans` : loans computed via middle::borrowck
  * `-Z flowgraph-print-moves` : moves computed via middle::borrowck::move_data
  * `-Z flowgraph-print-assigns` : assignments, via middle::borrowck::move_data
  * `-Z flowgraph-print-all` : all of the available sets are included.

Fix #15016.
Add low level support for polling with librustuv.

 * Adds functions for using arbitrary sockets with libuv
 * Adds types and functions required to support this.
auto merge of #15421 : catharsis/rust/doc-ffi-minor-fixes, r=alexcrichton

Signed-off-by: Anton Lofgren <alofgren@op5.com>
auto merge of #15604 : mrmonday/rust/raw-socket-libc, r=alexcrichton

This pull request adds some necessary function definitions and types for doing low level networking with Rust.
Deprecate `str::from_utf8_owned`

Use `String::from_utf8` instead

[breaking-change]
Deprecate `str::from_chars`

Use `String::from_chars` instead

[breaking-change]
Deprecate `str::from_char`

Use `String::from_char` or `.to_str` instead

[breaking-change]
Deprecate str::from_byte

Replaced by `String::from_byte`

[breaking-change]
Deprecate `str::from_utf16`

Use `String::from_utf16` instead

[breaking-change]
Deprecate `str::from_utf16_lossy`

Use `String::from_utf16_lossy` instead.

[breaking-change]
Deprecate `str::from_utf8_lossy`

Use `String::from_utf8_lossy` instead

[breaking-change]