Adds structural match tests for all range types.

Note: also adds the otherwise unrelated test `test_range_to_inclusive` for completeness

…ackline in source rendering

… the color escape characters

…r-output-color, r=jyn514

Rustdoc test compiler output color

Fixes rust-lang#72915

We just need to be sure it doesn't break rustdoc doctests' compilation checks. Maybe some other unforeseen consequences too?

r? `@ehuss`
cc `@rust-lang/rustdoc`

…rk-Simulacrum

Test structural matching for all range types

As of rust-lang#70166 all range types (`core::ops::Range` etc.) can be structurally matched upon, and by extension used in const generics. In reference to the fact that this is a publicly observable property of these types, and thus falls under the Rust stability guarantees of the standard library, a regression test was added in rust-lang#70283.

This regression test was implemented by me by testing for the ability to use the range types within const generics, but that is not the actual property the std guarantees now (const generics is still unstable). This PR addresses that situation by adding extra tests for the range types that directly test whether they can be structurally matched upon.

Note: also adds the otherwise unrelated test `test_range_to_inclusive` for completeness with the other range unit tests

…backline, r=jyn514

Ensure that the source code display is working with DOS backline

Fixes rust-lang#76361.

cc `@lzutao`
r? `@jyn514`

…GuillaumeGomez

Add tests and improve rendering of cfgs on traits

Shows the additional features required to get the trait implementation, suppressing any already shown on the current page. One interesting effect from this is if you have a cfg-ed type, implementing a cfg-ed trait (so the implementation depends on both cfgs), you will get the inverted pair of cfgs shown on each page:

![image](https://user-images.githubusercontent.com/81079/97904671-207bdc00-1d41-11eb-8144-707e8017d2b6.png)

![image](https://user-images.githubusercontent.com/81079/97904700-27a2ea00-1d41-11eb-8b9f-e925ba339044.png)

The hidden items on the trait implementation also now get the correct cfgs displayed on them.

Tests are blocked on rust-lang#78673.

fixes rust-lang#68100
cc rust-lang#43781

document that __rust_alloc is also magic to our LLVM fork

Based on [comments](rust-lang#79045 (comment)) by `@tmiasko` and `@bjorn3.`