Custom user sign-up model

[iqquee]

Right now, the sign-up user model being used for the user signup is a predefined user model which does not give a developer enough flexibility to add his/her own custom user model. A developer who wishes to use this package should be able to define their own user model for the user sign-up.
Currently this is the user model it uses for sign-up but I wish not to define a default user sign-up model for a developer.

There should be no user model defined, the user sign-up model should be what the developer who uses this package defined themselves.