Add support for patternProperties

[Balázs Édes]

patternProperties could come handy for something like the following schema part (borrowed from https://github.com/fungusakafungus/cloudformation-jsonschema):

"patternProperties": {
    ".*": {
        "type": "object",
        "properties": {
            "Value": {
                "type": "object"
            },
            "Description": {
                "type": "string"
            }
        },
        "required": ["Value"]
    }
}