new parameters for step_lencode_glm

[naveranoc]

In some situations, when you are modeling counts or GLM it is important to set an offset to the model. It would be interesting if step_lencode_glm allowed the user to specify the type of model needed (count, classification, etc.). In addition to allowing some offset to the model for the adjustment and estimation of the union of the different levels of the variable of interest.

Thanks