fashion mnist support

[moejoe95]

Hi,

first of all, thanks for this great project!

I noticed that in models/main.py (line 206) the fashion mnist dataset is called 'fashion-mnist'.

    # Deciding which dataset to use
    if cfg.dataset == 'mnist' or cfg.dataset == 'fashion-mnist':

But in capslayer/data/datasets/fashion_mnist it is called 'fashion_mnist', therefore main.py doesnt run with fashion mnist dataset.

Another thing:
in capslayer/data/datasets/fashion_mnist/writer.py MNIST_FILES should be FASHION_MNIST_FILES:

def load_fashion_mnist(path, split):
    split = split.lower()
    image_file, label_file = [os.path.join(path, file_name) for file_name in MNIST_FILES[split]]