memory optimize np array logic
memory optimize np array logic

Instead of keeping n arrays in memory until the end to average them, we
now just have a master array that all subsequent arrays are unary added
to, and then divided by the number of files processed

Also broke the averaging work into average(), and created exception
classes to call, rather than just printing our our woes. These two
things will lend well to forthcoming testing

DoWhileGeek/imgavg