This function reads the MNIST-Database, randomized it and saves it in the files "train" for the training data and "test" for test data.
readMNIST(folder)The location of the MNIST-Database files.
When the data is read the variables for the training data is trainData
and trainLabels and for the test data testData and
testLabels. To start the function
the files "train-images-idx3-ubyte", "train-labels-idx1-ubyte',
"t10k-images-idx3-ubyte", and "t10k-labels-idx1-ubyte" have to be in the
folder given by the parameter folder. The folder name must end with
a slash.