Add fzaninotto/faker as optional mocking engine

[ybelenko]

It would be great to use fakerphp/faker as fake data provider because:

1. It's well known stable solution with many features.
2. It supports seed to generate the same values in unit tests.
3. It generates real human examples in comparison to this package.
4. It can generate data for different locales.

The only disadvantage of fzaninotto/faker is library size(3.5MB). That's why I'm going to add it as suggest package, not required.

I submit this issue just to show what I'm working on right now!