Benchmarks: Fix class name

I somehow typoed the class name everywhere...
Benchmarks: Fix setup method calling

The previous means for finding the setup method wasn't working.

Also, the half hits setup method didn't work.
Add Local backend

This is a faster version of:

```php
$cache = new Matryoshka\Hierarchy([
   new Matryoshka\MemoryArray(),
   new Matryoshka\Memcache()
]);
```
Add getAndSetMultiple benchmarks
Local: Improve performance of getAndSetMultiple

Turns out replacing `$this->cache` with an `array_merge` of the existing
one with the found values was incredibly slow with a big cache because
it made a copy of the array. Looping over and setting them manually
speeds it up vastly for large caches.
Benchmarks: Add 1000 batch getMultiple variant
Backend: Add setMultiple

And override it for Local and Hierarchy to make it faster.
Merge local-backend (#2) into master

Local backend

This adds a `Local` backend that is a faster version of:

```php
$cache = new Matryoshka\Hierarchy([
   new Matryoshka\MemoryArray(),
   new Matryoshka\Memcache()
]);
```

There are also lots of other improvements/fixes to benchmarks that I came across.