Create a function that tweaks letters by one forward (+1) or backwards (-1) according to a list.
tweak_letters("apple", [0, 1, -1, 0, -1]) ➞ "aqold"
# "p" + 1 => "q"; "p" - 1 => "o"; "e" - 1 => "d"
tweak_letters("many", [0, 0, 0, -1]) ➞ "manx"
tweak_letters("rhino", [1, 1, 1, 1, 1]) ➞ "sijop"
Don't worry about capital letters.