Fixed error and improve count() in EMongoDocument + Added fields to find() allow return some certain fields only

Hi,
In your count() function:
```php
if($criteria instanceof EMongoCriteria)
	        $crtieria = $criteria->getCondition();
```
Misspelled here, right?
Also, I changed to:
```php
return $this->getCollection()->count($criteria);
```
Because it's better if you use count() of Mongo PHP driver than find() then return count of list.

About 
```php
public function find($criteria=array(), $fields=array())
```
Now, you can select return some certain fields only.

Regards,
Don