Revert "remove gflib"

This reverts commit 8b59909ac5.

gflib/blit.h

@@ -0,0 +1,17 @@
+#ifndef GUARD_BLIT_H
+#define GUARD_BLIT_H
+
+struct Bitmap
+{
+    u8 *pixels;
+    u32 width:16;
+    u32 height:16;
+};
+
+void BlitBitmapRect4BitWithoutColorKey(const struct Bitmap *src, struct Bitmap *dst, u16 srcX, u16 srcY, u16 dstX, u16 dstY, u16 width, u16 height);
+void BlitBitmapRect4Bit(const struct Bitmap *src, struct Bitmap *dst, u16 srcX, u16 srcY, u16 dstX, u16 dstY, u16 width, u16 height, u8 colorKey);
+void FillBitmapRect4Bit(struct Bitmap *surface, u16 x, u16 y, u16 width, u16 height, u8 fillValue);
+void BlitBitmapRect4BitTo8Bit(const struct Bitmap *src, struct Bitmap *dst, u16 srcX, u16 srcY, u16 dstX, u16 dstY, u16 width, u16 height, u8 colorKey, u8 paletteOffset);
+void FillBitmapRect8Bit(struct Bitmap *surface, u16 x, u16 y, u16 width, u16 height, u8 fillValue);
+
+#endif // GUARD_BLIT_H