To do:
- Allow matrix of designs in calcCrit
- 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
- long term goal: allowing for more general endpoint distributions
  (e.g. Bernoulli, negative-binomial, survival)
