Alpha version of slopes for GBStudio 3.2

Hi folks,

I have been trying to find more time to work on updating Platformer+ to work with the new version of GBStudio 3.2--which adds slope tiles to the platformer scene type. This update brings most of P+ up to date. However, there are still some difficult issues to make dashing work with slopes. Right now, dashing will stop when it hits a slope; or, if you have vertical momentum enabled, it will go through the slope tile. Hopefully I will be able to fix this in an upcoming release.

I've also added an updated version that does not include the new slope collision. Slopes are somewhat expensive in terms of additional processing, so if you don't plan to use them, then I would recommend using P+ version 1.7.

Last, but not least, I've recently released a book about the design of 2D Platforming games called Run and Jump. You can download the whole thing for free from MIT Press, or check it out here: https://hauntology.itch.io/run-and-jump