Add documentation to rotorcraft functions

[ybeyer]

• deadband.m
• mapActuatorToControlSurface.m
• bemQuasiStaticThrustFromTheta.m
• bemResponseAndControlDerivatives.m
• bemThetaFromDesiredThrustAndInflow.m
• bemThetaFromDesiredThrustCoefficentAndInflow.m
• bemThrustFromInflowParameters.m
• runRotorcraftAerodynamicsDemo.m (Rename it to something with 'example'?)