implement intesections + misc function options

TODO.md

@@ -1,14 +1,8 @@
 ## TODO:
 1. Function management
 	- Integrals between functions (too hard to implement, maybe will shelve)
-	- Display intersection between functions (would have to rewrite a lot of the function plotting handling)
-	- [Drag and drop support](https://github.com/emilk/egui/discussions/1530) in the UI to re-order functions
-	- Hide/disable functions
 	- Prevent user from making too many function entries
-	- Display function errors as tooltips or a warning box (not preventing the display of the graph)
-	- Clone functions
 2. Smart display of graph
-	- Display of intersections between functions
 3. Allow constants in min/max integral input (like pi or euler's number)
 4. Sliding values for functions (like a user-interactable slider that adjusts a variable in the function, like desmos)
 5. Fix integral display