Add some simple Classes

[jiming]

@mdeanda

From time to time, especially when do some new tech test or demo, we need use random Class. Only String is not enough.

What about add some random simple classes, such as Animal(Interface), Cat(class implement Animal), Dog(class implement Animal), and can make random of them.

BTW, I really like your lib, thanks a lot!

Jiming

[jiming]

Kind of like this one
https://github.com/cesarferreira/Pretender