improve clone_from_slice performance
add intmax
Part of #6993. Moved a bunch of uses of Ident to Name
Improve code in the intro.

All these stars aren't needed anymore.
auto merge of #18253 : steveklabnik/rust/small_doc_fixes, r=huonw

All these stars aren't needed anymore.
auto merge of #17683 : gereeter/rust/ident-to-name, r=pcwalton

This does a large chunk of #6993. It is based on top of #17654.
auto merge of #17960 : mahkoh/rust/clone_from_slice, r=pcwalton

Old vs. New vs. Vec::push_all

```
test slice     ... bench:   3091942 ns/iter (+/- 54460)
test slice_new ... bench:   1800065 ns/iter (+/- 69513)
test vec       ... bench:   1804805 ns/iter (+/- 75609)
```
Add a lint for not using field pattern shorthands

Closes #17792.
auto merge of #17896 : mahkoh/rust/intmax, r=alexcrichton

Closes #17075

I don't know if this is correct. The easiest way to find out is to run the following program on all targets but I can't do it myself.
```c
#include <stdint.h>
#include <stdio.h>

int main(void)
{
	if (sizeof(intmax_t) != 8) {
		puts("ERROR");
		return 1;
	}
}
```
auto merge of #17813 : P1start/rust/lint-field-shorthand, r=huonw

Closes #17792.
core: DSTify ImmutableSlice
core: DSTify MutableSlice
core: DSTify the rest of slice extension traits
core: DSTify StrSlice
unicode: DSTify UnicodeStrSlice
collections: DSTify StrVector
collections: DSTify slice extension traits
ascii: DSTify AsciiStr and AsciiExt
core: DSTify Repr
collections: DSTify CloneableVector