Add autoscale() method.

The autoscale() method sets the scale factor so that the value becomes unity. This is only possible for parameters with non-zero values.
Add autoscale() method.

The autoscale() method performs auto-scaling for all parameters in the spectral model. Auto-scaling means that the scale factor is that so that the value is unity.
Remove autoscale() and perform auto-scaling in parameter constructor.

The autoscale() method has been removed as it exists now in the GModelSpectral() base class.

The parameter constructor now calls autoscale() to perform an autoscaling of all model parameters.
Add autoscale() method.
Initial simple example ... to be finished.