variant_nested: easy dispatch chaining

[Llammissar]

I noticed the comment:
//TODO:support a.foo for a["foo"]?

Yes. But if possible I would seriously love for it to get taken a step further and work work with multiple levels. That is:

TomlNode root;
root.a.b.c = 42;
writeln(root.a.b.c); //Should print 42

I've actually been trying to get this very thing implemented off and on for weeks now, and the above snippet has been very elusive. From what I've found, getting it working one level deep is pretty easy; it's when you start trying to push it deeper that it sort of falls apart.

As of right now, I have two implementations: one with simple access but awful construction; one with simple construction but requiring an extra retrieval function at the end of the chain. (e.g.

root.a.b.c = 42;
writeln(root.a.b.c.val); //Prints 42

I'm pretty close to settling for the latter, but before that I'm going to try a few things with the code you have here-- if you have any thoughts on this, I'd love to hear them.

(Semi-related: what's the license for this repo?)

[timotheecour]

Ok, slowly getting back to it... sorry for delay.
For now:

one with simple construction but requiring an extra retrieval function at the end of the chain.

instead of val at the end, what about opCall, as I did here: https://github.com/timotheecour/dtools/blob/master/dtools/util/functional.d#L128

(Semi-related: what's the license for this repo?)

standard Apache V2