HabModel: A function to predict CPUE from a habitat equation
In rooperc4/MEHRSI: Habitat Model Estimates of Survey Abundances

This function uses the habitat model equation and parameter values from the hab_equation function to calculate a predicted CPUE. A dummy variable for a year effect is added from the yearp function using the year of the survey for each of the stations. The function also #' can incorporate a presence-absence prediction (defaults to 1 for present) #' from an external step (usually from the presence_absence function)

1	HabModel(variables, form, par, pred_pa = 1, year)

`variables`	Set of habitat variables to use in the modeling
`form`	for each variable, a form for the model equation (1, 2 or 3)
`par`	values for each of the parameters
`pred_pa`	the predicted presence or absence at each transect
`year`	year of the data collection