Simulation Changes

[coatless]

Issue:

We currently have a non-standard way of simulating models in R.

Furthermore, we need to provide a means to simulate values under heavy simulation.

Solution:

1. Change the simulation parameters from gen.gts(model, n) to gen.gts(n,model) to force the user to specify a value.
2. Write a gen.ts() function that does not add any bells and whistles of the gen.gts() function.