Every software I ever programmed follows bit.ly links once and insert the original url into the database. From then on, users can always go to the url directly. Don't hold your breath for the accuracy of bit.ly link tracking.

You can theoretically set up Google Analytics to follow outbound links.

https://support.google.com/analytics/answer/1136920?hl=en

Seems too complicated.

This is something that Medium itself could set up for you.

If you want something simpler, just paste this into your page: https://gist.github.com/5899046

Bit.ly is also useful in that you can use the same link across the web and have analytics all in one place. Otherwise you'd need to check medium to track links you posted there, and some other site for links from there etc.