New features

applyOnSlices, applyOnComplexSlices, mapOnSlices, mapOnComplexSlices: iterate over some dimensions and create slices along the other dimensions, and apply a function to these slices
prod: product over selected dimensions
accumulate: accumulate values along selected slices by a custom function
reduceSlices: similar to accumulate, but while accumulate uses a function that works on single elements, reduceSlices requires a function that accepts slices as an argument

Bug fixes