Support generics, add builtins like Partial

[ssalbdivad]

This is the API I'm envisioning:

scope({
    "box<t>": {
        box: "t"
    },
     boxedString: "box<string>"
})

There'd also be some way to define them using type syntax that I'll have to decide on, and a helper method like generic.

Could also consider adding higher-kinded types, maybe something like this:

scope({
    "box<t>": {
        box: "t"
    },
     // accepts a generic that takes one parameter, and creates a generic that applies it twice
     "nest<g><t>": "g<g<t>>",,
     "nestedBox": "nest<box>"
     "nestedString": "nestedBox<string>"
})

Generics should also be chainable from a type like this:

const myData = type({
  a: {
    x: number;
    y: string;
    z: {
      w: number;
    }
  },
  b: number;
  c: string;
})

const modifiedData = myData.optionalize("a|x|w").omit("a|y").merge({b: "string"})