native, rustuv: Fix spawning with empty args

There was a bug in both libnative and libuv which prevented child processes from
being spawned correctly on windows when one of the arguments was an empty
string. The libuv bug has since been fixed upstream, and the libnative bug was
fixed as part of this commit.

When updating libuv, this also includes a fix for #15149.

Closes #15149
Closes #16272
Update error message on compile
Single curly braces instead of double are being used
Add example of estimating pi using Monte Carlo simulation to std::rand
Add division by zero case to the `CheckedDiv` comment
Remove the dist function; it is more efficient to compare squared distances
rust.md: Explicitly point out how special `'static` is.

Drive-by: fix description of `&content` to point out that `&'f type`
is (as of today) only for type expressions.
API docs/examples for std::slice

 - API doc/example for next() in Permutations
 - API doc/example for permutations() in ImmutableCloneableVector
 - Moved examples for permutations and next into trait definition as
   comments on pull request #16244.
 - Fix erroneus inclusion of src/llvm in older commit.
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Update docs to use HTTPS for static.rust-lang.org addresses

cc #16123
Download snapshots using HTTPS

cc #16123
Guide: vectors
auto merge of #16429 : steveklabnik/rust/guide_vectors, r=cmr

Since https://github.com/rust-lang/rust/pull/16380 didn't get pulled in yet, I added it in here too.

This covers the very, very, very basics of vectors. I wanted to have a section that mentioned them, but I'm
unsure what else I should cover. So I just did the absolute simplest things. Feedback very welcome.
auto merge of #16427 : brson/rust/https, r=thestinger
auto merge of #16417 : jasonthompson/rust/docs/slice3, r=alexcrichton

- Moved examples for permutations and next into trait definition as
   comments on pull request #16244.
- Fixed (hopefully) issue with erronious commit of changes to src/llvm.
Fix many-crates-but-no-match test. (Issue #16348)
librustc: Use separate stack slot for each return.
Reenable ignored test and add run-pass test.
librustc: Add an intrinsic to retrieve the return pointer of a function.

This is needed for some GC stuff in Servo.
librustc: Don't allow return_address intrinsic in functions that don't use an out pointer.