Guide: generics
Allow generic foreign functions.

Generic extern functions written in Rust have their names mangled, as well as their internal clownshoe __rust_abi functions. This allows e.g. specific monomorphizations of these functions to be used as callbacks.

Closes #12502.
Add new tests for extern and foreign fns and name mangling.
Fix typo in the tutorial
Temporary bootstrapping hack: introduce syntax for r egion bounds like `'b:'a`,
meaning `'b outlives 'a`. Syntax currently does nothing but is needed for full
fix to #5763. To use this syntax, the issue_5763_bootstrap feature guard is
required.
auto merge of #16318 : nikomatsakis/rust/issue-5723-bootstrap-2, r=pnkfelix

Introduce syntax for lifetime bounds like `'b:'a`, meaning `'b outlives 'a`. Syntax currently does nothing but is needed for full fix to #5763. To use this syntax, the issue_5763_bootstrap feature guard is required.
Rename `Share` to `Sync`

This leaves the `Share` trait at `std::kinds` via a `#[deprecated]` `pub use`
statement, but the `NoShare` struct is no longer part of `std::kinds::marker`
due to #12660 (the build cannot bootstrap otherwise).

All code referencing the `Share` trait should now reference the `Sync` trait,
and all code referencing the `NoShare` type should now reference the `NoSync`
type. The functionality and meaning of this trait have not changed, only the
naming.

Closes #16281
[breaking-change]
auto merge of #15831 : rpjohnst/rust/generic-foreign-fns, r=alexcrichton

This allows for things like this:

    extern "C" fn callback<T>(t: T) { /* ... */ }
    extern "C" {
        fn take_callback(c: extern fn(i32));
    }

and later:

    take_callback(callback::<i32>);

Closes #12502.
Guide: closures
auto merge of #16317 : adrienbrault/rust/patch-1, r=kballard
Remove spawn-stack-too-big.rs, which is too flaky.
auto merge of #16334 : nikomatsakis/rust/mission-snapshot, r=achrichto
Guide: Traits
auto merge of #16206 : steveklabnik/rust/guide_lambdas, r=brson
auto merge of #16273 : steveklabnik/rust/guide_generics, r=brson
Cleanup collections::slice documentation.

This does a few things:

 - remove references to ~[] and the OwnedVector trait, which are both
   obsolete
 - correct the docs to say that this is the slice module, not the vec
   module
 - add a sentence pointing out that vectors are distinct from Vec
 - remove documentation on Vec.

closes #15459
auto merge of #16285 : alexcrichton/rust/rename-share, r=huonw

This leaves the `Share` trait at `std::kinds` via a `#[deprecated]` `pub use`
statement, but the `NoShare` struct is no longer part of `std::kinds::marker`
due to #12660 (the build cannot bootstrap otherwise).

All code referencing the `Share` trait should now reference the `Sync` trait,
and all code referencing the `NoShare` type should now reference the `NoSync`
type. The functionality and meaning of this trait have not changed, only the
naming.

Closes #16281
[breaking-change]
auto merge of #16279 : nham/rust/fix_slice_docs, r=alexcrichton

This does a few things:

 - remove references to ~[] and the OwnedVector trait, which are both
   obsolete
 - correct the docs to say that this is the slice module, not the vec
   module
 - add a sentence pointing out that vectors are distinct from Vec
 - remove documentation on Vec.

closes #15459
ast_map: Added iterator over all node id's that match a path suffix.

This is useful e.g. for tools need a node-id, such as the flowgraph
pretty printer, since it can avoids the need to first pretty-print the
whole expanded,identified input in order to find out what the node-id
actually is.

It currently only supports path suffixes thst are made up of module
names (e.g. you cannot use the type instantiation form `a::<int>::b`
or `option::Option::unwrap_or` as a path suffix for this tool, though
the tool will produce paths that have non-modulues in the portion of
the path that is not included in the suffix).

(addressed review feedback too)
refactored pprust::State constructor methods out from `pprust::print_crate`.

(Groundwork for pretty-printing only selected items in an input crate.)