Neutron-acceptance diagram shading

This makes jnads results equivalent to Monte-Carlo simulations but about 5 orders of magnitude faster for difficult modelling tasks.

The raw speed of NADS makes it a particularly attractive tool for beam modelling where evolutionary algorithms are used.

In strictly controlled tests, NADS and Monte-Carlo both produced identical results when simulating a SANS instrument.

If simulating an instrument takes more than one CPU-day, then performing a full optimisation of a neutron guide hall requires more than two CPU-decades.

NADS was designed with the goal of reducing the CPU time to less than one minute for all instrument geometries, making an optimisation of a neutron guide hall feasible within a week on a single desktop computer.