Move create_new_username() into bridge as static function

[NicoHood]

In order to avoid naming conflicts and to get a better idea from which lib we are creating a new user, all static functions should be moved into the Bridge class. Does this sound good to you?

[quentinsf]

Hi Nico -

In general, I agree, though there are enough people using the library now that I'd like to avoid backwards incompatibility where possible. So I think we should keep the module-level functions (some of which were contributed by others), even if they simply call class methods on the Bridge class. We can mark them as deprecated.

Feel free to send a pull request and I'll have a look.