Add option to use bcrypt

[andrejunges]

I know there is a way to pass it as a property when we initiate this module, but I don't think its fully compatible. When I tried to pass it, I got an error related to the provider not being a function.
Error line:
https://github.com/feathersjs/feathers-authentication/blob/master/src/index.js#L142

So it may be easier to the library itself provide a way to change the bcrypt implementation that's gonna be used.

[ekryski]

This is now possible and much more flexible. You can use the native bcrypt module by simply extending the verifier for feathers-authentication-local and implementing your own _comparePassword function that uses bcrypt. In fact, you can use any hashing function you would like.

You will also need to pass your own hash function as an option to the hashPassword hook.