Starts converting slice.hpp to use helper Slice
continuing development on slice...
Rough completion of slice conversion
Almost functioning conversion of slice
Adds description messages
Fixes a bunch of comments
adds test with imperfect step size
Handles case of uneven step size

with a slice like [0:5:3] the position isn't exactly equal to the end,
so the Slice::Iterator::operator!= has to handle that case
Merge branch 'sliceoflife'