Feat: add json output

[jianglu]

Add JSON output capability, the output result can be directly parsed by the jq JSON parser through a pipe

lok -o=json .

{
    "total": {
        "code": 111269,
        "comment": 66367,
        "blank": 17275,
        "file": 222,
        "size": "8.97 MB"
    },
    "items": [{
        "language": "Java",
        "code": 111101,
        "comment": 66367,
        "blank": 17250,
        "file": 221,
        "size": "8.96 MB"
    }, {
        "language": "Markdown",
        "code": 168,
        "comment": 0,
        "blank": 25,
        "file": 1,
        "size": "12.59 KB"
    }]
}

lok -o=json . | jq '.items[] | select(.language == "Java")'

{
  "language": "Java",
  "code": 111101,
  "comment": 66367,
  "blank": 17250,
  "file": 221,
  "size": "8.96 MB"
}

[wyhaya]

v0.2.5 has been released, thanks!