Rayleigh distribution for the TV+L0 decomposition (i.e. 2 variables) has now its
own class.

	It was previously on RiceDataTerm...

	* src/RayleighDataTerm2Vars.hh: New class here.
	* src/RayleighDataTerm2Vars.hxx: New class here.
	* src/main.cc: Use it.