JSON: Sort map keys before converting from Value to Json.

[prataprc]

NewValue(map).ToJson(jsn).Bytes() should return JSON string with keys sorted.

[prataprc]

JSON is also exposed to users via API. This means JSON Properties may not have its keys sorted.
Would be a good feature to implement:

• JSON->JSON with property keys sorted.

• JSON->CBOR with property keys sorted.

• For Values, JSON property is stored as map[string]interface{}, so no point is sorting it before converting to Value.

• For Collate, JSON properties are already sorted :)