Add JS partons

[Hendrik1704]

This implements the possibility to read in JETSCAPE parton output files with the Jetscape class in SPARKX. To switch to the parton mode there is a keyword argument called particletype in the constructor, which can be set to parton.
By default, it is set to hadron, such that the current behavior in any script used so far does not change.
This closes #180.
The corresponding documentation is added and the CHANGELOG is updated.

I tested this with one of my current parton output files. However, I will add some more rigorous testing methods for the Jetscape class in the tests for SPARKX. This is part of #147.

[NGoetz]

It looks good, I just wonder - does anything about particle class need to be changed for this? Like with respect to fractional charges etc. . Is the data represented correctly?

[Hendrik1704]

That is a good question, I have to check this. I just tested the reading of the input file. I guess I can just test the write to file function for some of the quantities. The other ones have to be tested by hand.
I think the PDGID package knows about quarks and their quantities. Maybe it is a problem that the charge is not int.

[Hendrik1704]

I did some further tests with the particle quantities:

print(had_epem_decays[0][0].ID) -> correct
print(had_epem_decays[0][0].pdg) -> correct
print(had_epem_decays[0][0].status) -> correct
print(had_epem_decays[0][0].E) -> correct
print(had_epem_decays[0][0].px) -> correct
print(had_epem_decays[0][0].py) -> correct
print(had_epem_decays[0][0].pz) -> correct
print(had_epem_decays[0][0].mass) -> correct
print(had_epem_decays[0][0].charge) -> wrong, always 0 (cast to int)
print(had_epem_decays[0][0].is_strange()) -> wrong, always gives False
print(had_epem_decays[0][0].is_heavy_flavor()) -> wrong, always gives False
print(had_epem_decays[0][0].spin()) -> correct
print(had_epem_decays[0][0].spin_degeneracy()) -> correct
print(had_epem_decays[0][0].is_hadron()) -> correct, always False
print(had_epem_decays[0][0].is_meson()) -> correct, always False
print(had_epem_decays[0][0].is_baryon()) -> correct, always False
print(had_epem_decays[0][0].compute_charge_from_pdg()) -> correct

I guess the charge function can be easily fixed. For the other functions it's probably more complicated. There we use the PDGID package.

[Hendrik1704]

This adds now a multiplication of parton charges by a factor 3 to make them integers. This is also reflected in the documentation. There are also tests for the Particle class added for this case and I test with Jetscape to read a parton file and filter for charged partons.

[NGoetz]

Thank you, this looks good!