A shopper tracks the prices of a few items every week. The prices come as a grid: one row per week and one column per item. The first row is week one.
They want to see how each price has moved since week one, as a percentage of that item's week-one price.
For an item whose week-one price was p, a later price q has changed by
per cent. A rise is positive and a fall is negative.
Task: write change_since_first(prices) and return a grid of the same shape, as a list of lists: every price turned into its percentage change since week one, rounded to 1 decimal place. The first row is all 0.0.
No week-one price is 0.