Guide: Fix inconsistency in 'Marcos' section

The old version switched in between examples from the value `5i` to `"Hello"`
and back. Additionally, the code generated by `rustc print.rs
--pretty=expanded` is not as verbose anymore.
auto merge of #17832 : brson/rust/updateversion, r=alexcrichton
auto merge of #16641 : steveklabnik/rust/intro_redux, r=alexcrichton

Because my '30 minute intro' was originally a blog post, the tone was a bit too light. It also was written a long time ago, and deserves a bit of a refresher for modern Rust. now that my work on the Guide is wrapping up, I want to give it a quick re-write as well.

This is not yet done, but I'm submitting it for feedback so far. I'd really like some comments on the ownership part in particular, which gets lower level than before, but is not strictly 100% accurate. Trying to strike a balance.

In general, I'm not sure I go into enough detail for those without systems experience, but am afraid of too much detail for those that do.

Rendered view: https://github.com/steveklabnik/rust/blob/intro_redux/src/doc/intro.md

/cc @wycats @nikomatsakis @brson etc
Add rustup.sh to the repo

Just to have it somewhere to point to. Updating it will not
automatically update the one on static.rust-lang.org.
Rename RELEASES.txt to RELEASES.md. It's markdown.
Update RELEASES.md for 0.12.0
Update AUTHORS.txt for 0.12.0
Update per feedback
Update html_root_url for 0.12.0 release
Fix keyword table

Markdown tables require a header, and we don't want one.

Fixes #17528
More relnotes tweaks
auto merge of #17834 : sfackler/rust/rustdoc-cfgs, r=alexcrichton,alexcrichton

Rustdoc would previously improperly handle key="value" style cfgs, which
are notably used for Cargo features.
auto merge of #17787 : bgamari/rust/fix-quote-method, r=huonw

The previous fix introduced in 75d49c8203405ab0af7a2b8b8698af02868fdbc2 neglected to parse outer attributes as described in #17782.
auto merge of #17836 : typelist/rust/guide-tuples, r=steveklabnik

Currently, the Guide says tuples "are only equivalent if the arity, types, and values are all identical", before presenting an example that uses `==` to compare two tuples whose arity and contained types match. This is misleading, because it implies that `==` can dynamically check whether two tuples have the same arity and contained types, whereas trying to do this would lead to a compiler error.

I tried to avoid destroying the flow of this section, but I'm not sure if I've been successful.
Add `abstract`, `final`, and `override` to reserved keywords
Fix unclear macros documentation.
Remove use of `final` and `override` (now reserved)
Add `abstract`, `final`, and `override` to rust.vim keyword list
Add tests for new reserved keywords `abstract`,`final`,`override`
auto merge of #17838 : vadimcn/rust/macros, r=alexcrichton