Include ChaCha pseudorandom generator
rust.css: Make it more clear when code spans are links
Add some notes about macro scoping
Use relative doc URLs in top-level guides
Update some old references to rust.md
Add a red-box warning to the macros guide
Add a guide to compiler plugins

Fixes #16983.
Link plugins guide from elsewhere
Disable the Roman numerals test on Android due to cross-compile issues
test: Don't depend on /bin/bash

Our FreeBSD bots apparently don't have bash installed, and it's ok to run with
sh anyway!

Unblocks a snapshot
syntax: Enable parsing of `const` globals

This rewrites them to the current `ItemStatic` production of the compiler, but I
want to get this into a snapshot. It will be illegal to use a `static` in a
pattern of a `match` statement, so all those current uses will need to be
rewritten to `const` once it's implemented. This requires that the stage0
snapshot is able to parse `const`.

cc #17718
auto merge of #16995 : kmcallister/rust/plugin-tutorial, r=alexcrichton

@steveklabnik, are you interested in looking this over?
Set the `non_uppercase_statics` lint to warn by default
Update the `unused` lint group to include more lints
Improve the `non_snake_case` lint to give better suggestions
Correct error message for invalid `ref`/`mut` bindings

Closes #15914.
Report trait/impl sig inconsistency before method/body inconsistency

Closes #15657.
Change rustc pretty-printing to print [T, ..n] instead of [T, .. n]
Move the lint for the stability lints to the method name only

Closes #17337.
tests: remove old compile-fail test asserting the removal of `const`.