Merge branch 'particle_splitting' into 'master'

doc/RTD/source/ParameterFiles/parameter_description.rst

examples/EAGLE_ICs/EAGLE_12/eagle_12.yml

examples/EAGLE_ICs/EAGLE_25/eagle_25.yml

examples/EAGLE_ICs/EAGLE_50/eagle_50.yml

examples/EAGLE_ICs/README

examples/EAGLE_low_z/EAGLE_12/eagle_12.yml

examples/EAGLE_low_z/EAGLE_25/eagle_25.yml

examples/EAGLE_low_z/EAGLE_50/eagle_50.yml

examples/EAGLE_low_z/EAGLE_6/eagle_6.yml

examples/parameter_example.yml

src/Makefile.am

src/chemistry/EAGLE/chemistry.h

src/chemistry/GEAR/chemistry.h

src/chemistry/none/chemistry.h

src/cooling/Compton/cooling.h

src/cooling/EAGLE/cooling.c

src/cooling/EAGLE/cooling.h

src/cooling/const_du/cooling.h

src/cooling/const_lambda/cooling.h

src/cooling/grackle/cooling.h