ME Chest: Fix drive item limit bug

Previously the math was incorrect, allowing a single 8k drive to store over 300,000 items. This also cleans up the storage area a bit, moving the API related to storage drives from the main API.lua to storage/api.lua.

modules/storage/api.lua

@@ -0,0 +1,48 @@
+-- storage/api.lua
+
+local BASENAME = "microexpansion"
+
+-- [function] register cell
+function microexpansion.register_cell(itemstring, def)
+  if not def.inventory_image then
+    def.inventory_image = itemstring
+  end
+
+  -- register craftitem
+  minetest.register_craftitem(BASENAME..":"..itemstring, {
+    description = def.description,
+    inventory_image = BASENAME.."_"..def.inventory_image..".png",
+    groups = {microexpansion_cell = 1},
+    microexpansion = {
+      drive = {
+        capacity = def.capacity or 5000,
+      },
+    },
+  })
+
+  -- if recipe, register recipe
+  if def.recipe then
+    -- if recipe, register recipe
+    if def.recipe then
+      register_recipe(BASENAME..":"..itemstring, def.recipe)
+    end
+  end
+end
+
+-- [function] Get cell size
+function microexpansion.get_cell_size(name)
+  local item = minetest.registered_craftitems[name]
+  if item then
+    return item.microexpansion.drive.capacity
+  end
+end
+
+-- [function] Calculate max stacks
+function microexpansion.int_to_stacks(int)
+  return math.floor(int / 99)
+end
+
+-- [function] Calculate number of pages
+function microexpansion.int_to_pagenum(int)
+  return math.floor(microexpansion.int_to_stacks(int) / 32)
+end