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.
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.
rustc: Remove ~[T] from the language

The following features have been removed

* box [a, b, c]
* ~[a, b, c]
* box [a, ..N]
* ~[a, ..N]
* ~[T] (as a type)
* deprecated_owned_vector lint

All users of ~[T] should move to using Vec<T> instead.