Default: Add savanna nodes, textures, crafting and fuels

mods/default/README.txt

mods/default/crafting.lua

mods/default/functions.lua

mods/default/nodes.lua

mods/default/textures/default_acacia_leaves.png

mods/default/textures/default_acacia_sapling.png

mods/default/textures/default_acacia_tree.png

mods/default/textures/default_acacia_tree_top.png

mods/default/textures/default_acacia_wood.png

mods/default/textures/default_dry_grass.png

mods/default/textures/default_dry_grass_1.png

mods/default/textures/default_dry_grass_2.png

mods/default/textures/default_dry_grass_3.png

mods/default/textures/default_dry_grass_4.png

mods/default/textures/default_dry_grass_5.png

mods/default/textures/default_dry_grass_side.png