Change harvest levels: wood mines weak stone, stone mines medium and
strong stone, iron mines very strong stone. Same for ores, except
strong ores require iron. Since hematite in banded iron formations and
magnetite veins in granite are strong, the player needs to get iron
from either magnetite sands or limonite clays.
Crafting stone tools now yields damaged tools, according to the stone
strength. Weak has the durability of gold, medium the durability of
wood, (very) strong yields full durability.
Fix replacement of some cobblestone recipes