A note to tileset authors concerning recent experimentals

A PR has been merged that changes the way some of the tileset and tile_config properties work ( https://github.com/CleverRaven/Cataclysm-DDA/pull/13151 ).

The ones already part of the game have been tweaked accordingly, but custom tilests will likely break if these changes aren’t implemented.

In the tileset.txt file:

Instead of "JSON: TilesetFolderExampleName/tile_config.json" it will now be "JSON: tile_config.json"

Instead of "TILESET: TilesetFolderExampleName/TilesetImageExampleName.png" it will now be "TILESET: TilesetImageExampleName.png"

In the tile_config.json file:

Instead of "“file”: “gfx/TilesetFolderExampleName/TilesetImageExampleName.png”," it will now be "“file”: “TilesetImageExampleName.png”,"

Instead of "“file”: “gfx/TilesetFolderExampleName/fallback.png”," it will now be "“file”: “fallback.png”,"

Fixes from @BevapDin will be in separate PR.

So at this moment paths in all new tileset must be related.
@chaosvolt @kevingranade please warm authors in IRC and forum.