Re-do the 30 minute intro

This was originally on my blog, so it's incredibly informal. Let's make
it better.
Handle emitting debug info for unboxed closures

This fixes an ICE.  Closes issue #17021
Build regression test for issue #17021 with -g

This causes it to hit the previously ICEing debuginfo codepath
Fix handling of struct variants in a couple of places

Fixes #17405.
Fixes #17518.
Fixes #17800.
update jemalloc

This includes optimizations to the thread cache and support for
shrinking and expanding huge (>4M) allocations in-place.
auto merge of #17414 : jakub-/rust/issue-17405, r=alexcrichton

Fixes #17405.
Fixes #17518.
Fixes #17800.
Rename the file permission statics in std::io to be uppercase

For example, this renames `GroupRWX` to `GROUP_RWX`, and deprecates the old
name. Code using these statics should be updated accordingly.
Remove the #[allow(non_uppercase_statics)] attr from bitflags!
Fixed iOS build (statics name lint)
auto merge of #17781 : P1start/rust/bitflags-lints, r=alexcrichton

Closes #17773.
rustdoc: make calls of markdown::render safer

Previously, external code might call `markdown::render()` without having
called `markdown::reset_headers()`, meaning the TLS key
`used_header_map` was unset.  Now `markdown::render()` ensures that
`used_header_map` is set by calling `reset_headers` if necessary.

Fix #17736
rustdoc: Correctly name lifetimes in bounds

Fix #16518
rustdoc: Support unboxed fn sugar in bounds
auto merge of #17803 : bkoropoff/rust/issue-17021, r=alexcrichton

This closes issue #17021.
rustdoc: Remove dummy UnknownBound variant
auto merge of #17812 : thestinger/rust/jemalloc, r=alexcrichton

This includes optimizations to the thread cache and support for
shrinking and expanding huge (>4M) allocations in-place.
auto merge of #17814 : vhbit/rust/ios-build-fix, r=huonw
rustdoc: Include lifetimes in re-exported bounds

Fix #17818
Add example to doc for `slice::ImmutableSlice::binary_search`.

Fix #17817.
syntax: Parse outer attributes in quote_method!

Fixes #17782.