To do
- allow for different maxEffs (and baselines)
  for planning
- allow for different clinical relevance thresholds for
  analysis
- add covariates into code
- allow for dose estimation with active control group
- add covMu argument for planning functions
- confint method for MCPMod
- Function to evaluate power and precision of the dose
  estimate (under a certain dose design) by simulation
- Function to interactively choose guesstimates
- Use of global optimization routines in case of 
  failed convergence for non-linear models
