Add HMGET support and WITHSCORES support for ZRANGE

Added HMGET support, and added WITHSCORES support for ZRANGE, with tests and readme update.

I also refactored the ZRANGEBYSCORE code a bit so that ZRANGEBYSCORE and ZREVRANGEBYSCORE could share code (sorry for the messy diff).
This test should be in two parts : one for `hmget` and one for `hgetall` : 
```php
	->string($redisMock->hmset('test', array(
		'test1' => 'somthing',
		'blabla' => 'anything',
		'raoul' => 'nothing',
	)))
		->isEqualTo('OK')
	->array($redisMock->hgetall('test'))
		->isEqualTo(array(
			'test1' => 'somthing',
			'blabla' => 'anything',
			'raoul' => 'nothing',
		))
	->integer($redisMock->expire('test', 1))
		->isEqualTo(1);
sleep(2);
$this->assert
	->array($redisMock->hgetall('test'))
		->isEmpty()
	->string($redisMock->hmset('test', array(
		'test1' => 'somthing',
		'raoul' => 'nothing',
	)))
	->array($redisMock->hmget('test', array('raoul', 'test1')))
		->isEqualTo(array(
			'raoul' => 'nothing',
			'test1' => 'somthing',
		))
	->integer($redisMock->expire('test', 1))
		->isEqualTo(1)
sleep(2);
$this->assert
	->array($redisMock->hmget('test', array('raoul', 'test1')))
		->isEqualTo(array(
			'raoul' => null,
			'test1' => null,
		));
```