In this kata you will have to write a function that takes litres and pricePerLitre
(in dollar) as arguments. Purchases of 2 or more litres get a discount of 5 cents per litre,
purchases of 4 or more litres get a discount of 10 cents per litre, and so on every two litres, up
to a maximum discount of 25 cents per litre. But total discount per litre cannot be more than 25
cents. Return the total cost rounded to 2 decimal places. Also, you can guess that there will not be
negative or non-numeric inputs.
1 Dollar = 100 Cents