Fix palette of Link and NPCs tiles

[kemenaran]

Link sprite sheet (and NPCs sprite sheets in general) are PNG files, but those are not easy to understand. For a start, the palette seems wrong.

Example of Link's PNG sprite sheet with an incorrect palette

We should edit these PNG sprite sheets to make them easier to edit–beginning with fixing the palette of the PNG files (while still compiling to the same .2bpp in the end).

How

rgbgfx seems to have support for alternate grayscale palettes. Probably the PNG files can be re-extracted using a better palette, and then rgbgfx invoked with the correct options would be able to compile the file back to the original .2bpp.

[kemenaran]

Based on a discussion with Aria Hiroshi 64, there should be an easy solution to this:

1. Import the PNG spritesheet into GIMP (or Glimse);
2. Index the image to 4 colors;
3. Change the color map colors (but without changing the color map order);
4. Save the PNG.

At compile time, rgbgfx will still use the color map in the order colors are declared, so it will still compile to the right 2bpp values.

(It seems this is how pokecrystal does it.)

[kemenaran]

(It seems ImageMagik can also be used to convert the PNG to indexed, then to change the colors.)

[ariahiro64]

Check my pull request #260