Unified framework for regularized functions

[fcasella]

The Modelica_Fluid library currently contains several functions (regRoot, regRoot2, etc.) which aim at approximating non-smooth functions with smooth approximation.
All these functions could be rewritten based on the theory of distribution, which might also help writing their derivatives.
Goal: develop a stand-alone package with examples, for later inclusion within Modelica_Fluid and possibly within Modelica.Math.