Pixpipejs

This does the following :

• open a local NIfTI/Minc2/MGH file, using pixpipe.FileToArrayBufferReader
• redirect the file buffer into a pixpipe.Image3DGenericDecoder to extract the dataset and metadata
• get the output as a generic pixpipe.Image3D object
• slice() the volume 3 times, along 3 given axis to get 3 pixpipe.Image2D objects
• display the images in separate canvas using a single instance of pixpipe.CanvasImageWriter