Shifted/doubled stitchpacks for texture atlas loading

[deathcap]

Added MC1.4-compatible pack (which I call 'stitchpack' to distinguish from MC1.5 'texturepack') per #3 - but there's still some difficulty using this so-called stitchpack with voxel.js, specifically:

https://github.com/shama/atlaspack tilepad:true pads with 1/2 of texture repeated on each side

https://github.com/deathcap/voxel-texture/ 4-tap sampling requires 2x2 repeated per tile <-- would be particularly useful with stitchpack.json coords, loading as "prebuilt atlas" ref shama/voxel-texture#14

[deathcap]

Decided not to do this, better to use https://github.com/deathcap/artpacks (and/or deathcap/artpacks#3)