The solution of the coding problem from the website: https://www.reddit.com/r/dailyprogrammer/comments/onfehl/20210719_challenge_399_easy_letter_value_sum/
Assign every lowercase letter a value, from 1 for a to 26 for z. Given a string of lowercase letters, find the sum of the values of the letters in the string.
lettersum("") => 0
lettersum("a") => 1
lettersum("z") => 26
lettersum("cab") => 6
lettersum("excellent") => 100
lettersum("microspectrophotometries") => 317