[Request] Allow for manually tweaking replacements for particular sets of VFlip and HFlip.

[frozenLake]

To give an example of what this could be used for, although divergent from the original game:

As you can see, at particular parts of the animation, the scythe flips over, breaking the consistancy of the animation slightly. It would be nice to be able to fix this, but this is a change that would require modifying the formatting of the manifest, so, that is a slight downside to be considered.

Other uses of this could be tweaking shading on flipped tiles, to account for the direction of a light source.

[shonumi]

Sorry for the late response. Anyway, it wouldn't change the manifest format as significantly as another EXT_ option. The key here is that the manifest already tracks what "type" of graphics is being used (BG or OBJ tile, DMG or GBC tile). Right now the type doesn't change for H/V flip, but it's trivial enough to add new types that represent stuff like DMG OBJ H-flip or GBC BG H+V flip. This method maintains backwards compatibility with the current manifest structure and existing graphics.

The only problem I see is that could potentially incur a performance penalty if over used.