Pixpipejs

This does the following :

• open a local Minc2 file, using pixpipe.FileToArrayBufferReader
• redirect the file buffer into a pixpipe.Minc2Decoder to extract Minc dataset and metadata
• get the output as a generique pixpipe.MniVolume 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