`facet` free y and x scales

[vincentarelbundock]

In plots like this one, it is sometimes useful to set different xlim or ylim on a per-facet basis. Is this possible now? Would it be hard to implement?

[grantmcdermott]

It's possible, see here: #90 (comment)

I was reluctant to do this originally (for reasons detailed at the link), but have encountered a few cases myself where free axis scaling for facets would be useful. So I'm open to revisiting.

[vincentarelbundock]

Cool cool. I'll think about this when I'm back at work.