My friend, that is an understatement. 
Joking aside, I agree. This Gateway Scripting Project concept was a major change that seems to have gotten lost in the shuffle. We apologize for the headaches that the outdated page caused.
I went rogue and created a quick replacement page: https://docs.inductiveautomation.com/display/DOC80/Project+Library
Additionally, I added a small heading and link on the Tag Event Scripts page linking back to the relevant information on the Project Library page, as you suggested. I'd like to spend a bit more time on the Project Library page and add some additional content (adding extra examples and such), but hopefully the changes on the page now should prevent folks from running into the same troubles.