I'm glad you enjoyed my demo!
As for how i made the collisions work, it was basically a bunch of math that boils down to "If Player is past the left side of the collision box, put them back into place" it does the job basically flawlessly, but may need to get improved for performance reasons (If possible, at least); The source code IS a bit of a mess currently, and i'm planning on rewriting it a bit when Friday comes around; Sound WILL be implemented, although it's not the biggest priority at the moment, i'll definitely TRY to implement it without third party libraries, but that's a problem for another time...
As for a Linux port, i'll see what i can do, and if i can handle Window Initialization and the Input system there, i'll be sure to port the engine here too!
As for a dev-log, likely somewhere around Saturday or Sunday where i'm most active, it'll be found on the Game Page itself