Readd tar block. Fixes #103

The proper way to resolve the redundancy between `building_blocks:Tar` and `moreblocks:tar` is with an alias in building_blocks as noted in issue #68.

The recipe conflict with streetsmod has been resolved by using `default:pine_tree` in place of `default:gravel`.  This may also be more realistic than gravel as a source of tar because pine derived tar was once of major economic importance.

crafting.lua

@@ -485,6 +485,10 @@ minetest.register_craft({
 	}
 })
 
+minetest.register_craft({
+	type = "cooking", output = "moreblocks:tar", recipe = "default:pine_tree",
+})
+
 minetest.register_craft({
 	type = "shapeless",
 	output = "moreblocks:copperpatina",