Re-do the 30 minute intro

This was originally on my blog, so it's incredibly informal. Let's make
it better.
syntax: Parse outer attributes in quote_method!

Fixes #17782.
doc: Update output of `rustc --version`
Properly handle cfgs in rustdoc

Rustdoc would previously improperly handle key="value" style cfgs, which
are notably used for Cargo features.
library-level docs for collections
add missing btree re-exports
Clarify that assigning/comparing different tuple types to one another won't compile
Re-exports core::str::Utf16CodeUnits in std::str

Closes #17751
Fix the most egregious instances of "local ambiguity: multiple parsing options..." error in macros, which often occurs when trying to match parts of Rust syntax.
For example, this matcher: `fn $name:ident( $($param:ident : $pty:ty),* )` would fail when parsing `fn foo()`, because macro parser wouldn't realize that an ident cannot start with `)`.

This resolves #5902, and at least partially mitigates #9364 and #3232.
auto merge of #17802 : Gankro/rust/collection-docs-redux, r=aturon

Adds a high-level discussion of "what collection should you use for what", as well as some general discussion of correct/efficient usage of the capacity, iterator, and entry APIs.

Still building docs to confirm this renders right and the examples are good, but the content can be reviewed now.
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
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.
auto merge of #17838 : vadimcn/rust/macros, r=alexcrichton
auto merge of #17840 : Sawyer47/rust/issue-17751, r=huonw

Closes #17751
add #[experimental] as_string/as_vec functions

This provides a way to pass `&[T]` to functions taking `&U` where `U` is
a `Vec<T>`. This is useful in many cases not covered by the Equiv trait
or methods like `find_with` on TreeMap.
auto merge of #17447 : thestinger/rust/silly_string, r=aturon

This provides a way to pass `&[T]` to functions taking `&U` where `U` is
a `Vec<T>`. This is useful in many cases not covered by the Equiv trait
or methods like `find_with` on TreeMap.