Added function to get a list of results from a provider

First of all, thank you for this great package. It's powerful yet simple. But I found something that could be really handy and yet is not there. I needed to sent templates to a printer with different data (that's where faker comes to place) and I noticed there was no way to just get a list of names or addresses. And I really needed this because making a loop inside my module would be pointless and I need this to be fast. So I created this little module that would return a list of any provider by the amount you want and with the specific function you want.

It's just as simple as:
```python
>>> from faker import Factory
>>> fake = Factory.create()
>>> fake.get_list_of('person', 5, 'name')
[u'Christian Greenholt', u'Jasen Dach', u'Dr. Magali Hansen', u'Mr. Cora Abbott V', u'Justice Hagenes']
>>> fake.get_list_of('company', 5)
[u'Batz-Blanda', u'Langworth-Kshlerin', u'Ankunding Ltd', u'Berge, Hessel and Hickle', u'Senger, Rowe and Haley']
```