Add notes about the shipping bin

docs/shipping_bin.md

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+### Shipping bin notes
+
+[svw:Shipping]: https://stardewvalleywiki.com/Shipping
+
+The "Full Shipment" achievement is awarded when the player has [shipped all items](svw:Shipping) in the "Items shipped (Farm & Forage)" tab of the Collections page (`CollectionsPage`) in the game menu.
+
+The game tries to give the achievement to the player when it displays the shipping summary menu (`ShippingMenu`) during the night. It uses `Utility.hasFarmerShippedAllItems` to check if the requirements are met. This means that the "Full Shipment" achievement can only be earned on nights during which the player has shipped some items.
+
+The "Full Shipment" achievement is achievement number 34. An item is shipped if it is present in thes `Game1.player.basicShipped` dictionary.
+
+There are 4 points at which the shipping items are determined:
+- In `Utility.getFarmerItemsShippedPercent` used by `ShippingMenu` via `Utility.hasFarmerShippedAllItems` to award the achievement
+- In the constructor of `CollectionsPage` to show the basic shipped items tab of collections page of the game menu
+- In `Utility.highlightShippableObjects` used by `ShippingBin.doAction` and `IslandWest.checkAction` to who shippable items when interacting with the shipping bin
+- In `Object.countsForShippedCollection` used by `ShippingMenu` via `ShippingMenu.parseItems` to select which items we track the shipping count
+
+**Utility.getFarmerItemsShippedPercent** goes through _Game1.objectInformation_ and keeps items that:
+- Are not artifacts: `!text.Contains("Arch")`
+- Are not fishing items: `!text.Contains("Fish")`
+- Are not minerals: `!text.Contains("Mineral")`
+- Are not gems (category): `!text.Substring(text.Length - 3).Equals("-2")` [note 1]
+- Are not cooking items: `!text.Contains("Cooking")`
+- Are not cooking (category): `!text.Substring(text.Length - 3).Equals("-7")` [note 1]
+- And are basicShipped items (see below): `Object.isPotentialBasicShippedCategory(...)`
+
+Where `text` is the 4th field of `ObjectInformation.json` representing the item type and category.
+
+\[note 1]: That code seems to always return true if I'm not mistaken?
+
+**CollectionsPage** goes through a sorted _Game1.objectInformation_ and keeps items that:
+- Are not artifacts: `if (text.Contains("Arch"))`
+- Are not fishing items: `else if (text.Contains("Fish"))`
+- Are not minerals or gems (category): `else if (text.Contains("Mineral") || text.Substring(text.Length - 3).Equals("-2"))` [note 2]
+- Are not cooking items or cooking (category): `else if (text.Contains("Cooking") || text.Substring(text.Length - 3).Equals("-7"))` [note 2]
+- And are basicShipped items (see below): `if (!Object.isPotentialBasicShippedCategory(...))`
+
+Where `text` is the 4th field of `ObjectInformation.json` representing the item type and category.
+
+\[note 2]: The `text.Substring(...).Equals(...)` code seems to always return false if I'm not mistaken?
+
+**Utility.highlightShippableObjects** calls `Object.canBeShipped` which keeps items that:
+- Are objects: `if (i is Object)`
+- Are not big craftables: `!this.bigCraftable`
+- Have a type, which (usually) excludes items that aren't normal objects or big craftables: `this.type != null`
+- Are not quest items: `!this.type.Equals("Quest")`
+- Can be trashed: `this.canBeTrashed()`
+- Are not furniture: `!(this is Furniture)`
+- Are not wallpapers: `!(this is Wallpaper)`
+
+Where `this` is an `StardewValley.Object`.
+
+**Object.countsForShippedCollection** checks the object's information and keeps items that:
+- Have a type, which (usually) excludes items that aren't normal objects or big craftables: `if (this.type == null ...)`
+- Are not artifacts: `if (... this.type.Contains("Arch") ...)`
+- Are not big craftables: `if (... (bool)this.bigCraftable)`
+- Have item id 433 (Coffee Beam) or...
+- Have a category: `case 0:`
+- Are not in the following categories:
+ - Seeds: `case -74:`
+ - Equipment: `case -29:`
+ - Furniture: `case -24:`
+ - Tackle: `case -22:`
+ - Bait: `case -21:`
+ - Junk: `case -20:`
+ - Fertilizer: `case -19:`
+ - Meat: `case -14:`
+ - Minerals: `case -12:`
+ - Crafting: `case -8:`
+ - Cooking: `case -7:`
+ - Gem: `case -2:`
+- Have an item index that is basicShipped (see below): `Object.isIndexOkForBasicShippedCategory`
+
+**Object.isPotentialBasicShippedCategory** checks the object's category and keeps items that:
+- Have item id 433 (Coffee Bean) or...
+- Have a category `case 0:`
+- Are not in the following categories:
+ - Seeds: `case -74:`
+ - Equipment: `case -29:`
+ - Furniture: `case -24:`
+ - Tackle: `case -22:`
+ - Bait: `case -21:`
+ - Junk: `case -20:`
+ - Fertilizer: `case -19:`
+ - Meat: `case -14:`
+ - Minerals: `case -12:`
+ - Crafting: `case -8:`
+ - Cooking: `case -7:`
+ - Gem: `case -2:`
+- Have an item index that is basicShipped (see below): `Object.isIndexOkForBasicShippedCategory`
+
+**Object.isIndexOkForBasicShippedCategory** checks that the object id:
+ - Is not 434 (Stardrop)
+ - Is not 889 (Qi Fruit)
+ - Is not 928 (Golden Egg)
+
+Other functions of note:
+- **ShippingBin.shipItem** and **Farm.shipItem** adds the item to the shipping bin
+- **Game1.player.shippedBasic** keeps track of shipped items statistic