Enable specifying list type in computed fields

[lucperkins]

As far as I can tell, it isn't possible to specify the of type of lists in computed fields the way that you can in non-computed fields. Thus, this is possible:

fields: {
  tags: {
    type: "list",
    of: { type: "string" },
    default: []
  }  
}

But this is not:

computedFields: {
  segments: {
    type: "list",
    of: { type: "string" },
    resolve: (doc) => { ... }
  }
}

Instead, you can only specify an untyped list, and in the generated output you end up with this:

segments: list

But this raw list type isn't defined!

There may be reasons to explicitly disallow typed lists in computed fields, and if so I'd be curious why! Otherwise, this feels like an oversight to me.

[schickling]

I agree there are definitely some gaps in regards to which types can be used for computed fields. This will be addressed before 1.0 is released. (Also see #149)

[lucperkins]

@schickling Sounds great. I look forward to it!