Add test for cmontecarlo function macro_atom
Add test for cmontecarlo function macro_atom

The fixture model_3lvlatom is added, which provides
macro atom data (references, transition probabilities etc.)
for a simple 3 level atom (including internal jumps and
branching).

kaushik94/tardis,kaushik94/tardis,kaushik94/tardis,kaushik94/tardis