README: Mark API for engine properties as finished

Author: adazem009

README.md

@@ -124,7 +124,7 @@ Button {
 - [x] JPEG and PNG rendering
 - [x] Everything related to displaying sprites (position, rotation, size, etc.)
 - [ ] Loading projects in another thread
-- [ ] API for engine properties (FPS, turbo mode, etc.)
+- [x] API for engine properties (FPS, turbo mode, etc.)
 - [ ] Loading projects from URL
 - [ ] SVG rendering
 - [ ] Mouse position