Add support for different initial-state hadrons in the CLI

[cschwan]

No description provided.

[alecandido]

I don't know exactly what's your purpose, but in case you want to do it for comparisons (show two columns aside for the two PDFs), maybe you might consider to have multiple PDFs, instead of two (just a list of space separated IDs).

For sure, there are cases in which it might not be possible, but sometimes might be relatively simple to do it.

Just a suggestion :)

[cschwan]

The idea is to support processes with different hadronic initial states, for instance proton-lead collisions, for which support in the CLI (and only there) is missing. Of course, eventually we'd like to generalize it to multiple 'PDFs', see here: #172.

[alecandido]

Sorry, my bad. I just misunderstood the purpose of the issue.

[cschwan]

No worries, it made me realize that the title is confusing!