Decoding JSON array

[florianreinhart]

It's currently not possible to decode a JSON array using MySQLDataDecoder.

Changing MySQLDataDecoder.swift from

private final class _Decoder: Decoder {
    func unkeyedContainer() throws -> UnkeyedDecodingContainer {
        fatalError()
    }
}

to

private final class _Decoder: Decoder {
    func unkeyedContainer() throws -> UnkeyedDecodingContainer {
        throw DoJSON()
    }
}

fixes this.