[Bugfix] Model JSON value type properly

[mike-north]

The current ambient type definitions are inappropriately constrained here

pretender/index.d.ts

Line 28 in 7101a31

export type ResponseData = [number, { [k: string]: string }, string];

This would not allow for arrays, or non-string values.

I've made a package containing a "JSON value" type defined as

export type Primitive = string | number | boolean | null;
export interface Object {
	[member: string]: Value;
}
export interface Arr extends Array<Value> {}

export type Value = Primitive | Object | Arr;

that models characteristics of JSON values correctly