Runs a uniform box exposed to constant cooling rates computed with 
the Grackle library.

To run with Grackle mode 0, configure swift with:
  ./configure --with-cooling=grackle_0 --with-grackle=$GRACKLE_ROOT

To run with Grackle mode 1, configure swift with:
  ./configure --with-cooling=grackle_1 --with-grackle=$GRACKLE_ROOT
  
To run with Grackle mode 2, configure swift with:
  ./configure --with-cooling=grackle_2 --with-grackle=$GRACKLE_ROOT
  
To run with Grackle mode 3, configure swift with:
  ./configure --with-cooling=grackle_3 --with-grackle=$GRACKLE_ROOT