Allow different ANEOS EoS

[gassmoeller]

This should allow a fix for #35. I found a simpler solution than I was afraid was necessary. By removing the constness of the ANEOS EoS, we can let every scenario (GI, test, whatever) create their own ANEOS equations of state and then use that when assigning equations of states to particles. I did not make it an input parameter yet, but @TylerLaBree and @mnakajima7 you should be able to follow the same steps you did in #34 to make this work. Could you pick this branch up and do the rest of the work? Let me know if something does not work out.

[TylerLaBree]

Will do. Is the idea that the user specifies the EoS in the input file using a string, or do we need them to specify the actual EoS using something like this?

ANEOS_EoS.push_back(EoS::IdealGas <PS::F64>(1.4));

[gassmoeller]

Let them specify an EoS filename in the input file, and the EoS can then read that file (ANEOS_EoS.push_back(EoS::IdealGas <PS::F64>(aneos_filename));). Also stick to one EoS for now, we can think about adding another one (e.g. for the core) later.

[TylerLaBree]

I think this allows the user to specify the chart for the AnEoS, but I think we would also like to be able to specify whether to use AnEoS, Tillotson, or IdealGas. Do you have a preferred method to do this?