Added functions CalculateDiffractionFilter() and CalculateDiffractionFilterCoefficient() for the calculation of the Diffraction transfer function and the diffraction coefficient, as well as the function CalculateDiffractionFactor() for the calculation of the (frequency dependent) diffraction factor without the influence of the path length.

Finishing renaming of Kirchhoff to Maekawa method and making some interface changes for a more simple usage of the Maekawa methods

In the function Generate(), added calculation of the sound energy decrease due to the path length as well as the phase shift.

Added function Generate() (work in process) as well as functions ApplyEmitterModel() and ApplySensorModel().

Added the function ApplyAcousticModels() and therefore the function ApplyDiffractionModel() and ApplyReflectionModel().