Add support for a new output format : GeoJSON

[fulups]

• add new GeoJSON output format

{
    "type": "FeatureCollection",
    "features": [
        {
            "type": "Feature",
            "geometry": {
                "type": "Point", "coordinates": [118.0,9.0,54]
            },
            "properties": {"aaa": "test 1","bbb": 1,"ccc":"2012-01-01:00:00.000Z", ...},
        },
        {
            "type": "Feature",
            "geometry": {
                "type": "Point", "coordinates": [14.0,2.0,12]
            },
            "properties": {"aaa": "test 2","bbb": 2,"ccc":"2012-01-01:00:00.000Z", ...},
        }
    ]
}

• update README for this new format

• update test cases for this new format