librustc: Allow coercions through arrays.
it -> Cargo

It wasn't clear if we needed to install Hello World or Cargo.
librustc: Don't ICE on binding same field multiple times in struct
pattern.
Little typo fix

- ./hello_world which is not recognized on Windows fixed.
- .exe extension added.
- Little rewriting.
fix typo in readme
auto merge of #15262 : zecozephyr/rust/15620, r=luqmana

Fixes #15260
auto merge of #15259 : steveklabnik/rust/patch-3, r=alexcrichton

It wasn't clear if we needed to install Hello World or Cargo.
std: make sure HashMap from_iter uses random initialization by default

It turns out that HashMap's from_iter implementation was being
initialized without the sip keys being randomized. This adds
a custom default hasher that should avoid this potential vulnerability.
std: micro optimize Hash{Map,Set}::{new,with_capacity}
auto merge of #15267 : ruud-v-a/rust/patch-1, r=huonw

[This commit](https://github.com/rust-lang/rust/commit/25fe2cadb10db1a54cefbd1520708d4397874bc3#diff-04c6e90faac2675aa89e2176d2eec7d8R57) forgot to remove one line.
Fix distcheck

libcoretest wasn't being included which broke the verification of the
tarball.
add example for from_byte() documenation
auto merge of #15275 : sfackler/rust/distcheck, r=alexcrichton

libcoretest wasn't being included which broke the verification of the
tarball.
Add `utf16_units`

This deprecates `.to_utf16`. `x.to_utf16()` should be replaced by either
`x.utf16_units().collect::<Vec<u16>>()` (the type annotation may be optional), or
just `x.utf16_units()` directly, if it can be used in an iterator context.

Closes #14358

[breaking-change]
auto merge of #14613 : schmee/rust/utf16-iterator, r=huonw

Closes #14358.

~~The tests are not yet moved to `utf16_iter`, so this probably won't compile. I'm submitting this PR anyway so it can be reviewed and since it was mentioned in #14611.~~ EDIT: Tests now use `utf16_iter`.

This deprecates `.to_utf16`. `x.to_utf16()` should be replaced by either `x.utf16_iter().collect::<Vec<u16>>()` (the type annotation may be optional), or just `x.utf16_iter()` directly, if it can be used in an iterator context.

[breaking-change]

cc @huonw
Add `impl Show for &Show`

This makes printing a `Show` trait object much easier.
JSON cleanup

* Tried to make the code more idiomatic
* Renamed the `wr` field of the `Encoder` and `PrettyEncoder` structs to `writer`
* Replaced some `from_utf8` by `from_utf8_owned` to avoid unnecessary allocations
* Removed unnecessary `unsafe` code
Removed unnecessary Box
Add `encode` and `decode` shortcut functions

Now you can just use `json::encode` and `json::decode`, which is very
practical

**Deprecated `Encoder::str_encode` in favor of `json::encode`**

[breaking-change]
Implement FromStr for Json