Add property args structure.

[ghost]

This PR adds a structure to keep all the run args in a single place. This will allow us to more easily add support for #25.

/cc @moodmosaic @TysonMN

[moodmosaic]

I think this looks good, however, perhaps we can merge once we're done with #296, unless @TysonMN has a better idea.

[ghost]

I think this looks good, however, perhaps we can merge once we're done with #296, unless @TysonMN has a better idea.

That works for me 👍🏼

[TysonMN]

Also looks good to me. I think we should merge now instead of waiting for #296.