Convert CEL files to CL2 at load time. CL2 format is more efficient and is about as fast to render.
CEL vs CL2 sizes, on dLvl 5: https://gist.github.com/glebm/9bbdd76962abcd4fd2405ecd3379af97
Memory:
* Peak memory (while loading): -300 KiB
* Memory in-game (dLvl5): -700 KiB
* RG99 binary size: -15 KiB (1333096 -> 1317192)
Performance on rg99:
* On average, -1 FPS in town.
* Same FPS in dungeon (20 FPS on dLvl 1).
This OOB happened when rendering a sprite so that it is exactly
off-screen (touching the border but not visible) on top/bottom
while also being only partly off-screen on the left or right.
Makes `CelSprite` unowned and adds a new `OwnedCelSprite` class for
owned sprites.
This clarifies ownership and makes the code cleaner in a number of
places.
Additionally, because the `CelSprite` class is now tiny (1 less
pointer), we can pass it by-value instead of by-reference, removing a
pointer indirection in the rendering functions.
Gleb Mazovetskiy