Add laws.

[sellout]

E.g.

• Birecursive#iso should pass the monocle.Iso laws.
• x.ana(f).cata(g) ≟ x.hylo(g, f) (for some generic f and g)
• x.cata(g) ≟ x.hylo(g, _.project) and its dual
• either make other operations (gcata, futu, etc.) final or add laws comparing them to the default impls

[yilinwei]

@sellout Do you mind if I take a stab at this? I'd like to do this issue at the same time as this one here

[sellout]

Yeah, that would be awesome.

Feel free to poke me if you run into anything confusing on the Matryoshka side of things. I’m more than happy to help out.

[yilinwei]

Just a comment to show I haven't forgotten about this; hopefully will have something out fairly soon.