yzziizzy/minetest_bitumen: Adds bitumen to minetest, including tar sands, oil shale, refineries, and some basic generators

Izzy fdcc77edf2 cement mixer, concrete tweaks		%!s(int64=5) %!d(string=hai) anos
..
cement_mixer.obj	095e48f4e2 better organization	%!s(int64=6) %!d(string=hai) anos
oil_derrick.obj	095e48f4e2 better organization	%!s(int64=6) %!d(string=hai) anos
sphere.obj	5bbfa4eb07 spherical tank	%!s(int64=6) %!d(string=hai) anos
storage_tank.obj	fdcc77edf2 cement mixer, concrete tweaks	%!s(int64=5) %!d(string=hai) anos