Adds ANARCHY-PU Scheme

This MR adds the ANARCHY-PU scheme.

Let's see what Jenkins has to say about this one. I will follow up in the next 12-24 hours with some final check plots, so please wait to merge until we've seen those. Feel free to take a look at the code changes though, as there are a few ones in the core.

doc/RTD/source/SubgridModels/EAGLE/index.rst

@@ -236,7 +236,7 @@ implicit problem. A valid section of the YAML file looks like:
      H_reion_z:            11.5      # Redhift of Hydrogen re-ionization
      He_reion_z_centre:     3.5      # Centre of the Gaussian used for Helium re-ionization
      He_reion_z_sigma:      0.5      # Width of the Gaussian used for Helium re-ionization
-     He_reion_eV_p_H:       2.0      # Energy injected in eV per Hydrogen atom for Helium re-ionization.
+     He_reion_ev_p_H:       2.0      # Energy injected in eV per Hydrogen atom for Helium re-ionization.
 
 And the optional parameters are: