generateMuons creates muons coming from the vertex flying in direction phi in r/phi plane with inclination lambda. The particles are MCParticles for use as input for the PrimaryIonisationProcessor. Usage: generateMuons energy phi lambda nEvents [outfile.slcio] * Use 0..2pi to define a fixed phi angle. Negative phi gives random angle. * Lambda range is -pi .. pi * Outfile name is optional, default is MCMuons.slcio * Energy is in GeV