feat(jsondiff): Add support for preserving Unicode characters in jsondiff CLI

[hirmiura]

Mostly same as #127.
This is also for jsondiff.

Example:
t1.json: {"test": "test"}
t2.json: {"test": "テスト"}

Without the support:

$ jsondiff t1.json t2.json 
[{"op": "replace", "path": "/test", "value": "\u30c6\u30b9\u30c8"}]

With the support:

$ jsondiff -u t1.json t2.json
[{"op": "replace", "path": "/test", "value": "テスト"}]

[stefankoegl]

Thanks for the contribution :)