Add date palm

Spawns in hot and dry desert, but requires water. This makes it a bit harder to
find, but where found, it can be more abundant.
If found in the middle of a desert, its presence indicates a water source below
the surface.

As an additional optional feature, dates (slowly) grow back after harvesting.

biome_defs.lua

@@ -24,6 +24,40 @@ moretrees.palm_biome = {
 	max_count = 10,
 }
 
+moretrees.date_palm_biome = {
+	surface = "default:desert_sand",
+	avoid_nodes = moretrees.avoidnodes,
+	avoid_radius = 10,
+	seed_diff = 339,
+	min_elevation = -1,
+	max_elevation = 10,
+	near_nodes = {"default:water_source"},
+	near_nodes_size = 20,
+	near_nodes_count = 100,
+	near_nodes_vertical = 20,
+	temp_min = -0.20,
+	humidity_max = 0.20,
+	rarity = 10,
+	max_count = 30,
+}
+
+moretrees.date_palm_biome_2 = {
+	surface = "default:desert_sand",
+	avoid_nodes = moretrees.avoidnodes,
+	avoid_radius = 10,
+	seed_diff = 340,
+	min_elevation = 11,
+	max_elevation = 30,
+	near_nodes = {"default:water_source"},
+	near_nodes_size = 1,
+	near_nodes_count = 1,
+	near_nodes_vertical = 30,
+	temp_min = -0.20,
+	humidity_max = 0.20,
+	rarity = 10,
+	max_count = 30,
+}
+
 moretrees.apple_tree_biome = {
 	surface = "default:dirt_with_grass",
 	avoid_nodes = moretrees.avoidnodes,