Add toString() method

[simPod]

I like to work with my objects in clean OOP way and therefore also trying to avoid using magic methods as __toString().

So I added toString() method so the API is nicer, more fluent and expressive

- (string) Stringy::create($name)->camelize();
+ Stringy::create($name)->camelize()->toString();

[voku]

In my fork there is already the "toString" method: https://github.com/voku/Stringy#tostring

... maybe you give it a try. :)

[simPod]

@voku Thanks! I'd prefer to use original repo tho if possible. However, it seems it's not maintained anymore :/