This adds minimal command support to enable Gakuen King's music mode:
- P: Set text color
- I: Allow user to select a grid item using mouse/keyboard input
- Y25: Switch text window
- Y118: Set text X coordinate
- Y119: Set text Y coordinate
The meanings of these commands were investigated from the implementation
of Gakuen King's system3.5 port.
Before this, the virtual VRAM was 32 bits per pixel, with each pixel
holding an 8-bit index color or 0x80RRGGBB. The latter was for Ayumi-
chan Monogatari Jisshaban, which has been unsupported since system3-sdl2
was forked from System3 for Win32.
This change removes the 0x80RRGGBB format and makes the virtual VRAM 8
bits per pixel.
Before this change, fade in and fade out was implemented using a
16-steps dithering pattern.
Now fading uses alpha-blending. It behaves like the PC98 version, where
fading was done by palette animation.
This reduces `sizeof(AGS)` by 1.2MB.
kichikuou