cfunction
(array/pop arr)
Remove the last element of the array and return it. If the array is
empty, will return nil. Modifies the input array.
(def a @[1 2])
(array/pop a) # => 2
a # => @[1]
(array/pop a) # => 1
a # => @[]
(array/pop a) # => nil
a # => @[]