rustdoc: Hyperlink cross-crate reexports

This should improve the libcore experience quite a bit when looking at the
libstd documentation.
doc: Fix some broken links
Register new snapshots
auto merge of #14068 : alexcrichton/rust/rustdoc-xcrate-links, r=brson

This should improve the libcore experience quite a bit when looking at the
libstd documentation.
Reexport wchar_t, c_schar
auto merge of #14073 : alexcrichton/rust/snapshots, r=huonw
shootout-nbody improvements

- minimize bound check
- factorise operations
- use x, y, z instead of [f64, ..3]
- ~1.15 faster
auto merge of #14081 : Manishearth/rust/c-schar-reexport, r=huonw

Don't merge this until #14076 merges, since it is based on top of that branch to avoid merge conflicts.
add back jemalloc to the tree

This adds a `std::rt::heap` module with a nice allocator API. It's a
step towards fixing #13094 and is a starting point for working on a
generic allocator trait.

The revision used for the jemalloc submodule is the stable 3.6.0 release.

Closes #11807
add an align parameter to exchange_malloc

Closes #13094
use jemalloc to implement Vec<T>
initial port of the exchange allocator to jemalloc

In stage0, all allocations are 8-byte aligned. Passing a size and
alignment to free is not yet implemented everywhere (0 size and 8 align
are used as placeholders). Fixing this is part of #13994.

Closes #13616
fix Vec<ZeroSizeType>
vec: move some code inside alloc_or_realloc
vec: factor out some deallocation code
gitattributes: rm obsolete jemalloc entry
rename `global_heap` -> `libc_heap`

This module only contains wrappers for malloc and realloc with
out-of-memory checks.
rustdoc: Fix search links to enums/typedefs

When the values in html::item_type were updated, the JS definitions were
accidentally not updated as well.

Closes #14095
remove the word managed from the trait explanation
pass correct CFLAGS for jemalloc