app skeleton
Everything but the bonus
Finished bonus round - custom validaiton and tagging
Add 'week3/day3/url_shortener/' from commit '9ad6ead4606f15aab1afc9988a9e5eaa4fd3b5e6'

git-subtree-dir: week3/day3/url_shortener
git-subtree-mainline: 8a61ef4040aacf22dbb7f57031dbf9001fd59718
git-subtree-split: 9ad6ead4606f15aab1afc9988a9e5eaa4fd3b5e6
Partner attribution