update identifier naming warnings to give an example

This updates identifier warnings such as ``struct `foo_bar` should have a
camel case identifier`` to provide an example.

Closes #14738.
Add detection of dead struct fields
Remove the dead code identified by the new lint
Mark relevant structs with repr(C)
Converted PortReader and ChanWriter to use Vec.
auto merge of #14765 : rapha/rust/master, r=alexcrichton
core: Rename `container` mod to `collections`. Closes #12543

Also renames the `Container` trait to `Collection`.

[breaking-change]
auto merge of #14740 : P1start/rust/name-warnings, r=alexcrichton

This updates identifier warnings such as ``struct `foo_bar` should have a
camel case identifier`` to provide an example.

Closes #14738.
core: Move the collections traits to libcollections

This commit moves Mutable, Map, MutableMap, Set, and MutableSet from
`core::collections` to the `collections` crate at the top-level. Additionally,
this removes the `deque` module and moves the `Deque` trait to only being
available at the top-level of the collections crate.

All functionality continues to be reexported through `std::collections`.

[breaking-change]
auto merge of #14709 : alexcrichton/rust/collections, r=brson

This is mostly just a cosmetic change, continuing the work from #14333.
Moved integer trait and functions to submodule
Cleanup bigint
librustc: Implement overloading for the call operator behind a feature
gate.

This is part of unboxed closures.
std: Read HOME instead of USER

Apparently one of the linux bots doesn't have the USER variable defined, and
this fix will likely land more quickly than a fix to the bots.
Add missing repr(C) annotations to mutex.rs
auto merge of #14775 : alexcrichton/rust/fix-master, r=brson

Apparently one of the linux bots doesn't have the USER variable defined, and
this fix will likely land more quickly than a fix to the bots.
Implement #[plugin_registrar]

See RFC 22.

[breaking-change]
Use phase(plugin) in bootstrap crates

Do this to avoid warnings on post-stage0 builds.
Use phase(plugin) in other crates
Use phase(plugin) in tests