Composite multiple PPI params at once

[barthoekstra]

Currently the composite_ppi() function only composites PPIs for a single parameter.

I need to make composites of a bunch of parameters stored in some PPIs, which obviously I'd like to do all at once rather than separately and then rebuilding a single composite PPI. So I've tweaked the composite function to accept a vector of param names (similar to how param selection in read_pvolfile() works) and a vector of method names to set methods per parameter type (if necessary).

As this is a ‘prototype’ function, I was wondering if you're interested in including this functionality (if you're not already working on it anyways). If so, even though I'm not 100% sure I'll end up using it myself, I could contribute and improve my existing code to make composite PPIs of multiple parameters.

[adokter]

Hey @barthoekstra, yes this would be very useful and was on the todo-list, so please make a PR, thanks!

[barthoekstra]

Ok. Work in progress.

[adokter]

closed by #393