add embossing effect to generated hammer heads

Idea by texmex

https://gitlab.com/tacotexmex
https://forum.minetest.net/viewtopic.php?p=349194#p349194

system/register_hammer.lua

@@ -64,6 +64,7 @@ uniham.register_hammer = function (short_id, definition)
             ['+h'] = definition.head,
             ['+m'] = 'uniham_head_mask.png'
         })
+        texture = '(('..texture..')^(uniham_emboss.png^[opacity:51.2))'
     end
 
     if definition.texture then

textures/README.md

@@ -1,3 +1,3 @@
-All textures are licensed unter CC-BY-SA 4.0 or later
+All textures are licensed under CC-BY-SA 4.0 or later
 
 https://creativecommons.org/licenses/by-sa/4.0/legalcode