Changing the way convolution/pooling layers work. They now do VALID convolution by default, and a new option to add padding is included. This is not a backwards compatible change unfortunatelly, and a way to convert to the old way is to add pad: attribute to every conv layer and pad with half the size of filters. For example, if filter size was 5 with old code, add pad:2 and the code will run exact same. The pooling layer also takes the pad: parameter but that's less common to see in practice.