Removed PANDA-Ex.R file. This last one should not be committed (script built by R check process)
minor changes: use of the same length of time tabulation in fit_env_bd as first study.
removed useless debbuging print
Added possibility to not use df argument in fit_env_bd
updated fit_env_bd documentation due to recent changes
fixed minor numerical bug within the fit_env_bd (step function parameters)
Remove Vectorize in Phi & Psi. Vectorize increase CPU time