* Move append_vec bench to the crate with append_vec
* Use black_box to tell the compiler not to optimize away test data
```
pub fn black_box<T>(dummy: T) -> T {
unsafe {
let ret = std::ptr::read_volatile(&dummy);
std::mem::forget(dummy);
ret
}
}
```
* Revert "Use black_box to tell the compiler not to optimize away test data"
This reverts commit 5610b8ee957f1d8bf6e270e392859e8b23b1e472.
* Use black_box to tell the compiler not to optimize away test data
* Create bench directories
878a842611