Generation of stochastic processes with evaluate function

[marcobehrendt]

The evaluate function in spectralrepresentation requires a DataFrameRow. That means that currently only one process realisation can be generated at a time and if more process realisations shall be generated, a for-loop is required. Maybe it might be worthwhile to change the evaluate function that also multiple process realisation can be generated in one step.

[mbvoyager]

I agree that another multiple dispatch that supports DataFrames directly would increase user friendlyness and looks nicer.

[FriesischScott]

I'm making some changes here. The spectral representation shouldn't even be using DataFrame inputs at all. I'm reworking it so the inputs are vectors and matrices for evaluation of multiple processes.

DataFrames should only be used when a Model is involved.