code: public RequestToken signup(int flags, BaasHandler<BaasUser> handler) {
          return signupWithStrategy(flags,DefaultSignupStrategy.INSTANCE,handler);
      }
docs: Asynchronously signups this user to baasbox
  using provided password and priority
  
  @param flags {@link RequestOptions}
  @param handler  an handler to be invoked when the request completes
  @return a {@link com.baasbox.android.RequestToken} to manage the asynchronous request