Add option to specify reporters

There should also be configuration options to select any of the reporting types, which should include:

• JSON
• Console
• HTML

Proposed JSON output format:

{
    "summary": {
        "passed": 1,
        "failed": 1,
        "completed": 1,
        "passed with warnings": 1
    },
    "results": [
        {
            "url": "https://www.test.com",
            "tests": [
                {
                    "name": "does not have console errors",
                    "result": "failed with warnings",
                    "data": "<JSON representation of an array of object>"
                },
                {
                    "name": "should not have a horizontal scrollbar",
                    "result": "passed"
                },
                {
                    "name": "should load page within 3 sec",
                    "result": "failed"
                },
                {
                    "name": "identify external dependencies",
                    "result": "completed",
                    "data": [
                        {
                            "dependencyUrl": "https://somewhere.com/file.js"
                            "downloadedLocation": "/some/location/somewhere_com_file.js"
                        }
                    ]
                },
            ]
        }
    ]
}

Valid results are passed, failed, and warning.