Define a new setting g:rust_fold

g:rust_fold allows folding to be enabled. This lets the user turn on
folding without having to define autocommands.
Set softtabstop, textwidth, and optionally colorcolumn

Setting softtabstop makes <Del> delete 4 spaces as if it were a tab.

Setting textwidth allows comments to be wrapped automatically. It's set
at 80, which is the recommended line length for Rust programs. There are
suggestions that it should be 79, but our current style guide says 80 so
that's what we're matching.

A new setting g:rust_colorcolumn sets colorcolumn as well, to +1,101.
This indicates both the textwidth and the second stricter line length of
100 that our style guide lists.
Remove rust_colorcolumn, set textwidth to 99

The latest change to aturon/rust-guidelines states that lines must not
exceed 99 characters. This gets rid of the 80/100 split, so we don't
need to customize colorcolumn amymore.
mandelbrot: fix overlapping buffers
Fix cargo install instructions

Cargo now comes with Rust
Support for specifying the code model

The default code model is usually unsuitable for kernels,
so we add an option to specify which model we want.
mk: Fix LD_LIBRARY_PATH_ENV_NAMES in cross build
obsolete.rs: fix typo in message
rustc.1: fix typo

Uses the same wording as ``config.rs`` now.
complement-lang-faq.md: fix typos
debuginfo: Add python formatters that allow LLDB to print values with Rust syntax
debuginfo: Inject 'Rust-mode' LLDB prelude into debuginfo test scripts.
debuginfo: Remove atexit()-debugger shutdown from lldb_batchmode.py

The shutdown call would always result in an exception being printed to standard error.
debuginfo: Add LLDB autotests to debuginfo test suite.

This commit adds LLDB autotests to the test suite but does not activate them by default yet.
debuginfo: Make sure that only one LLDB test task is run at a time.

Some older versions of LLDB have problems with multiple instances running in parallel. This commit makes sure we don't do that.
debuginfo: Don't crash when encountering global variable with unknown source span.
Add an option to disable the use of the redzone

Disabling the redzone is required in x86-64's kernel mode to avoid interrupts trashing the stack.
auto merge of #15693 : steveklabnik/rust/guide_fix_cargo, r=cmr

Cargo now comes with Rust!
Examples for Integer trait methods.
Main example for bigint usage.

Also use `///` for documentation instead of `/**`. End comments with
`.`.

Show imports for bigint example.

They might be useful.