Add formatter for MozLog v2

[leplatrem]

Usage:

[formatter_generic]
class = mozsvc.util.MozLogFormatter

Schema:

{  
    "type":"object",
    "required":["Timestamp"],
    "properties":{
        "Timestamp":{
            "type":"integer",
            "minimum":0
        },
        "Type":{
            "type":"string"
        },
        "Logger":{
            "type":"string"
        },
        "Hostname":{
            "type":"string",
            "format":"hostname"
        },
        "EnvVersion":{
            "type":"string",
            "pattern":"^\\d+(?:\\.\\d+){0,2}$"
        },
        "Severity":{
            "type":"integer",
            "minimum":0,
            "maximum":7
        },
        "Pid":{
            "type":"integer",
            "minimum":0
        },
        "Fields":{
            "type":"object",
            "minProperties":1,
            "additionalProperties":{
                "anyOf": [
                    { "$ref": "#/definitions/field_value"},
                    { "$ref": "#/definitions/field_array"},
                    { "$ref": "#/definitions/field_object"}
                ]
            }
        }
    },
    "definitions":{
        "field_value":{
            "type":["string", "number", "boolean"]
        },
        "field_array":{
            "type":"array",
            "minItems": 1,
            "oneOf": [
                    {"items": {"type":"string"}},
                    {"items": {"type":"number"}},
                    {"items": {"type":"boolean"}}
            ]
        },
        "field_object":{
            "type":"object",           
            "required":["value"],
            "properties":{
                "value":{
                    "oneOf": [
                        { "$ref": "#/definitions/field_value" },
                        { "$ref": "#/definitions/field_array" }
                    ]
                },
                "representation":{"type":"string"}
            }
        }
    }
}