Add support for json file output

[bkbilly-intrack]

Outputs a json file in this format:

{
    "url": "http://testphp.vulnweb.com/artists.php",
    "query": "artist=1",
    "data": null,
    "injections": [
        {
            "parameter": "artist",
            "paramtype": "GET",
            "injection": [
                {
                    "type": "boolean-based blind",
                    "payload": "artist=1 AND 6109=6109",
                    "vector": "AND [INFERENCE]"
                },
                {
                    "type": "time-based blind",
                    "payload": "artist=1 AND (SELECT 4409 FROM (SELECT(SLEEP(5)))lyNY)",
                    "vector": "AND (SELECT [RANDNUM] FROM (SELECT(SLEEP([SLEEPTIME]-(IF([INFERENCE],0,[SLEEPTIME])))))[RANDSTR])"
                },
                {
                    "type": "UNION query",
                    "payload": "artist=-3053 UNION ALL SELECT NULL,CONCAT(0x7170627871,0x6d714b436c56464c6c7056644c4c4d6a6f414d705a44554c6f5058474b475954545552684471566a,0x7162787871),NULL-- -",
                    "vector": " UNION ALL SELECT NULL,[QUERY],NULL-- -"
                }
            ]
        }
    ]
}