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

Izzy fdcc77edf2 cement mixer, concrete tweaks		6 gadi atpakaļ
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cement_mixer.obj	095e48f4e2 better organization	7 gadi atpakaļ
oil_derrick.obj	095e48f4e2 better organization	7 gadi atpakaļ
sphere.obj	5bbfa4eb07 spherical tank	7 gadi atpakaļ
storage_tank.obj	fdcc77edf2 cement mixer, concrete tweaks	6 gadi atpakaļ