Added a class BioMedication (enabling drug adm)

  Drug release with a concentration 'Dose' is modelled by a
  Gamma distribution,

     y_adm' = Dose * beta^2 * t * exp( -beta*t ) - clRate * y_adm

  hence the parameter alpha = 2 of the Gamma distribution is fixed,
  and the clearance rate is given by 'clRate'.  The parameter 'beta'
  can be used to model specific pharmacokinetic properties of the
  applied drug.