Sorry for the late reply; I was away from home, but just checked out the Linux version and read the Devlog.
Cool stuff, very impressed by the size and lack of external dependencies. What are your external includes/libraries?
Two suggestions that I have:
I noticed that the window has both the enlarge and scale options available, but the engine doesn't resize to the new size. The window API you're using should have some sort of flags or functions to disable these options, or you should be able to grab the current window size through an API function, but either way; learning those flags or functions will just give you a little more control for the engine.
I also noticed that one of the maps contains a slope and through Debug mode; I saw that it was created with multiple tiles. It works, but I figure that adding sloped tiles would stop over-draw and be more efficient. You could even allow sliding based off the normal of the slope. I remember THIS article helped me a lot when I was making an AABB vs AABB platformer in the past. Lots of good stuff that's easy to implement in that article.
I'll definitely keep an eye on the project. I'm a big fan of people coding their own engines :D