Fix various sentence fragments, missing articles, and other grammatical
issues in the documentation for write! and writeln!.

Also fix the links (and link names) for common return types.

armv7l is armv7 architecture and CFG_CPUTYPE should be armv7 in order to end up
with armv7-unknown-linux-gnueabihf.mk rather than
arm-unknown-linux-gnueabihf.mk

Use arm-unknown-linux-gnueabihf for hardware floating point armv6 variant

Fixes rust-lang#36788.

…anics

…ation.

case with different lifetime with spans

 - Elide lifetimes to increase the readability
   of `DerefMut` examples

Prevent exhaustive matching of Ordering to allow for future extension

The C++11 atomic memory model defines a `memory_order_consume` ordering which is generally equivalent to `memory_order_acquire` but can allow better code generation by avoiding memory barrier instructions. Most compilers (including LLVM) currently do not implement this ordering directly and instead treat it identically to `memory_order_acquire`, including adding a memory barrier instruction.

There is currently [work](http://open-std.org/Jtc1/sc22/wg21/docs/papers/2016/p0098r1.pdf) to support consume ordering in compilers, and it would be a shame if Rust did not support this. This PR therefore reserves a `__Nonexhaustive` variant in `Ordering` so that adding a new ordering is not a breaking change in the future.

This is a [breaking-change] since it disallows exhaustive matching on `Ordering`, however a search of all Rust code on Github shows that there is no code that does this. This makes sense since `Ordering` is typically only used as a parameter to an atomic operation.

Improve "Doesn't live long enough" error

case with different lifetime scope

issue rust-lang#36537 part of rust-lang#35233
r? @jonathandturner

…teln, r=alexcrichton

Copyediting on documentation for write! and writeln!

Fix various sentence fragments, missing articles, and other grammatical issues in the documentation for write! and writeln!.

Also fix the links (and link names) for common return types.

(Noticed when preparing rust-lang#37472 ; posted separately to avoid mixing the new documentation with copyedits to existing documentation.)

Misc fixes for configure

Currently,
`./configure` at armv6 machines ends up with

```
configure: error: unknown CPU type: armv6l
```

`./configure` at armv7 machines **silently** produces build for armv6 (compatible, but suboptimal)

```
configure: CFG_BUILD            := arm-unknown-linux-gnueabihf
```

Use quieter test output when running tests on Travis CI.

Fixes rust-lang#36788.

Remove unused type aliases

Found by extending the dead code lint. The lint itself is work in progress because of false positives.

cc rust-lang#37455.

Add missing space in mutable_transmutes lint

…r=nikomatsakis

ICH: Hash expression spans if their source location is captured for panics.

Since the location of some expressions is captured in error message constants, it has an influence on machine code and consequently we need to take them into account by the incr. comp. hash. This PR makes this happen for `+, -, *, /, %` and for array indexing -- let me know if I forgot anything.

In the future we might want to change the codegen strategy for those error messages, so that they are stored in a separate object file with a stable symbol name, so that only this object file has to be regenerated when source locations change. This strategy would also eliminate unnecessary duplications due  to monomorphization, as @arielb1 has pointed out on IRC. I opened rust-lang#37512, so we don't forget about this.

r? @nikomatsakis

…tracking-issue, r=alexcrichton

Add tracking issue number to Result::unwrap_or_default unstable annotation.

Implemented in rust-lang#37299.

Tracking issue: rust-lang#37516.

… r=bluss

Elide lifetimes in DerefMut documentation

 - Elide lifetimes to increase the readability of `DerefMut` examples