Add ROR strategy

[giacrossi]

Add recursive order reduction strategy as implemented in G.A. Gerolymos, D. Senechal, and I. Vallet,
Very-High-Order WENO Schemes, AIAA 47. Aerospace Sciences Meeting, Orlando, [ FL, USA], Jan. 5-8, 2009

[giacrossi]

The ROR strategy should be applied in the software that uses the WenOOF library, not in the library itself, because this library is independent from the reconstructed/interpolated variables, while the ROR strategy uses density and pressure variables to reduce the order of the reconstruction if a smooth stencil isn't found. What do you think @szaghi?