replace farming with submodule

.gitmodules

mods/farming

mods/farming/README.txt

mods/farming/api.lua

mods/farming/depends.txt

mods/farming/hoes.lua

mods/farming/init.lua

mods/farming/nodes.lua

mods/farming/textures/farming_bread.png

mods/farming/textures/farming_cotton.png

mods/farming/textures/farming_cotton_1.png

mods/farming/textures/farming_cotton_2.png

mods/farming/textures/farming_cotton_3.png

mods/farming/textures/farming_cotton_4.png

mods/farming/textures/farming_cotton_5.png

mods/farming/textures/farming_cotton_6.png

mods/farming/textures/farming_cotton_7.png

mods/farming/textures/farming_cotton_8.png

mods/farming/textures/farming_cotton_seed.png

mods/farming/textures/farming_desert_sand_soil.png