write fetch-from-fridge and fetch-from-pantry
Exercise 3 - part 1

Write a function fetch-ingredient which
takes the name of an ingredient and an
amount and fetches that amount of the
ingredient. Also make it accept just the
ingredient, with a default amount of 1.
Exercise 3 - part 2
Exercise 3 - part 3
Exercise 3 - part 4
Exercise 3 - part 5
Exercise 3 - part 6