Add `bench_llio`
Add `bench_llio`

This module implements some basic benchmarks for the `Llio` module,
using `core_bench`.

The benchmark assumes there's a baseline implementation in the
`Llio_orig` module (make a copy of `llio.ml` and `llio.mli` to
`llio_orig.ml` and `llio_orig.mli` before making your changes).

You can build to executable using

```
$ ocamlbuild -use-ocamlfind -package core_bench -I tools bench_llio.native
```

Then run `./bench_llio.native -help` for some documentation.

Incubaid/arakoon,Incubaid/arakoon,openvstorage/arakoon,openvstorage/arakoon,Incubaid/arakoon,openvstorage/arakoon