To do:
- allow for dose finding with active control  
- additional methods for bootMCPMod objects (plot, summary method)
- calculation of lower bound on design criterion (for validating
  numerically found optima)
- Function to interactively choose guesstimates
- Add Bayesian (and bootstrap?) fitting capabilities in gFitDRModel?
- Add a way to model dose-time-response data (i.e. add a way of
  handling missing data) for commonly encountered endpoints
  (e.g. normal, binary, time-to-event)?
- Extend calcOptDesign to non-normal data (standardize according to number of 
  parameters for D-optimal design)
- Add function to perform sample size calculation for nonlinear
  dose-response modelling
- Add possibility to fit placebo corrected dose-response estimates with
  gFitDRModel