Memory manufacturers and AAA game studios hate her!
With some clever rearranging, PTGB now uses only 36 KiB of the 64 KiB
BG VRAM. This means the remaining 28 KiB is free to use in the future.
Caveats: The flex tileset must not use more that 6 KiB. There is a check
for it added.
VRAM Map
06000000 - 06000800 ( 2K): Eternal backdrop and textbox tileset
06000800 - 06002000 ( 6K): Flex BG tileset
06002000 - 06002400 ( 2K): BG0: Backdrop tilemap
06002800 - 06003000 ( 2K): BG1: Flex BG tilemap
06003000 - 06003800 ( 2K): BG2: Textbox tilemap
06003800 - 06004000 ( 2K): BG3: Text tilemap
06004000 -~06009000 (20K): Text rendering bitmap
06009000 - 06010000 (28K): Free work RAM
06010000 - 06018000 (32K): Sprite tileset
Additionally:
- Explicitly clear VRAM on boot
- Dirty workaround to fix box drawing buffer overflow.
- Flex backgrounds use a table instead of a huge switch statement
- Textbox tile IDs are now const u16[] instead of int[]
