This update was apparently more than just a level editor:
Some changes: a new nexus overworld system
We’ve redesigned the nexus layout -- we found that the previous one was not very friendly for beginners. A surprisingly small fraction of players actually ventured outside of the forest area! Additionally, the distribution of door difficulty was not even, so new players often ended up in places way over their skill level. This new layout splits up the nexus into four sub-nexuses (nexii?): Forest, Mansion, City, and Lab. Also, the easy doors are easier to get to, and the gold doors are harder to reach.
New key progression system
Along with the nexus change, we also reworked the key system. The problem with the old key system was that it rendered non-SS scores useless. However, it was good in that it highly rewarded perfection. This new system is more accessible without taking away the satisfaction of a perfect score. It works like this:
Think of the scores as percentages: an S is worth 50%, an A is worth 40%, all the way down to 10% for a D. So an SS is worth 100%, an SA is worth 90%, etc.
Your top scores in each level are combined to determine your key count: every 100 percentage points you earn, you get a key. For example, if you get an AB (70%) on one level, and a SA (90%) on another, you get a key, and the 60% remainder is applied to your next key.
This works on a per-key-type basis. So you have a separate meter for silver keys, gold keys, etc.