Wrap recursive Rust types into Box

[kossnocorp]

Recursive types like this one cause Rust to fail to compile:

Json: JsonNull | JsonBoolean | JsonNumber | JsonString | JsonArray | JsonObject | JsonUnion | JsonLiteral | JsonTuple

JsonBase: {
  doc?: string
}

JsonNull: {
  ...JsonBase,
  kind: "null"
}

JsonBoolean: {
  ...JsonBase,
  kind: "boolean"
}

JsonNumber: {
  ...JsonBase,
  kind: "number"
}

JsonString: {
  ...JsonBase,
  kind: "string"
}

JsonArray: {
  ...JsonBase,
  kind: "array",
  descriptor: Json
}

JsonObject: {
  ...JsonBase,
  kind: "object",
  properties: [JsonProperty]
}

JsonProperty: {
  ...JsonBase,
  kind: "property",
  name: string,
  descriptor: Json,
  required: boolean
}

JsonUnion: {
  ...JsonBase,
  kind: "union",
  descriptors: [Json]
}

JsonTuple: {
  ...JsonBase,
  kind: "tuple",
  descriptors: [Json]
}

JsonLiteral: {
  ...JsonBase,
  kind: "literal",
  value: string | int | float | boolean
}

Using Box where appropriate solves it:

pub struct JsonArray {
    pub doc: Option<String>,
    pub kind: JsonArrayKindArray,
    pub descriptor: Box<Json>,
}

[kossnocorp]

Depends on #9 implementing the definitions dependency tree.