API docs/examples for std::slice

 - API example for move_from in MutableVectorAllocating
 - API doc/example for next() in Permutations
 - API doc/example for permutations() in ImmutableCloneableVector
You should be able to do something like this:

```
cd /path/to/repo/rust
git checkout -b your-branch
cd src/llvm
git reset --hard 0d999e5b315b6ff78fcea772466d985ce53fd8dc
cd ../..
git add src/llvm
git commit --amend
```