Better WAD2 implementation

[ericwa]

• Supports quake and hexen 2 (they both use WAD2, with the palette in gfx/palette.lmp, but the palette colors are different)
• Handles different open documents using different palettes correctly
• If you change the gamedir in the game configuration, the palette isn't reloaded until you close/reopen the document, or open a new document

I didn't add anything to disable this code if the game is GoldSrc; it always tries to load gfx/palette.lmp in the Document constructor, but this could be surrounded by a check for the game engine type.

[LogicAndTrick]

I think it'd probably be cleaner to branch in the switch instead of here, maybe something like this?

case WadEntryType.Texture:
    textureDataOffset = MoveToTextureData(br, out width, out height);
    paletteSize = br.ReadUInt16();
    paletteDataOffset = br.BaseStream.Position;
    break;
case WadEntryType.QuakeTexture:
    textureDataOffset = MoveToTextureData(br, out width, out height);
    paletteSize = 256;
    paletteDataOffset = 0;
    break;

...

private long MoveToTextureData(BinaryReader br, out uint width, out uint height)
{
    br.BaseStream.Position += 16; // Skip name
    width = br.ReadUInt32();
    height = br.ReadUInt32();
    var textureDataOffset = br.BaseStream.Position + 16;
    var num = (int)(width * height);
    var skipMapData = (num / 4) + (num / 16) + (num / 64);
    br.BaseStream.Position += 16 + num + skipMapData; // Skip mipmap offsets, texture data, mipmap texture data
    return textureDataOffset;
}

[ericwa]

Agreed, I refactored it like that.