Function default_builder 

pub fn default_builder<D>() -> DecoderBuilder<D, GrayImage, String>
where
    D: GenericImageView<Pixel = Rgba<u8>>,

Create a default DecoderBuilder

It will use the following components:

• prepare: BlockedMean
• locate: LineScan
• extract: QRExtractor
• decode: QRDecoder

The builder can then be customised before creating the Decoder