Fit dict

cc @licode 
@tacaswell @licode We need to figure out how to get the docstring format that we need for these models (especially Gaussian and Lorentzian) but still keep lmfit's ability to guess the parameters of the model.  In the previous version of `physicss_function.py` we had the correct docstring so that it could be autowrapped into vistrails but were missing the ability to guess the model parameters. In this version of `physics_function.py` we have the ability to guess the model parameters but these cannot be autowrapped into vistrails.