mod_rank bug

[sallyrobson]

found some places where we were improperly defining mod_rank which was causing issues in mod order. mod_rank() should dispatch on a type not on a modification itself so the definition should look something like:
mod_rank(::Type{<:CustomMod})

not mod_rank(m::CustomMod)

[Ethan-Russell]

We don't have any mods that allow you to set their rank as an input, but we may want to do that eventually. If we are requiring that to be in the type, we will have to parameterize the type, as in below:

struct MyCustomMod{R}
    field1
    field2
    function MyCustomMod(field1, field2, rank)
        return new{rank}(field1, field2)
    end
end

[Ethan-Russell]

This was closed in #198