feat(TypeScript): add JsonCompatible type

More general than Object -- modern JSON serializers also support direct
string, number, boolean, etc.

src/core/JsonCompatible.ts

@@ -0,0 +1,8 @@
+type JsonCompatible =
+    | string
+    | number
+    | boolean
+    | { [x: string]: JsonCompatible }
+    | JsonCompatible[]
+
+export default JsonCompatible

src/core/JsonObject.ts

@@ -1,5 +1,7 @@
+import JsonCompatible from './JsonCompatible.js'
+
 interface JsonObject {
-  data: Object
+  data: JsonCompatible
 }
 
 export default JsonObject

src/core/index.ts

@@ -10,6 +10,7 @@ export { default as BinaryStream } from './BinaryStream.js'
 export { default as TextFile } from './TextFile.js'
 export { default as BinaryFile } from './BinaryFile.js'
 export { default as JsonObject } from './JsonObject.js'
+export { default as JsonCompatible } from './JsonCompatible.js'
 
 export { default as TypedArray } from './TypedArray.js'
 export { default as IntTypes } from './IntTypes.js'