There are three executables, compiled with different options:

1. wombat_check is compiled with compiler checks switched on and
   optimisation switched off; use ful for debugging, not meant for
   routine use

2. wombat_sequential is optimised, but uses a single thread only

3. wombat_parallel is optimised and uses multiple threads - BUT
   requires making an Intel OMP library available; see
   https://software.intel.com/en-us/articles/redistributables-for-intel-parallel-studio-xe-2015-composer-edition-for-os-x
