adds OtherProducts and Collections data structures

MODELS.md

@@ -372,9 +372,14 @@ struct Video {
 
 # Collection
 
-A Collection represents one or more Albums and/or Tracks that are offered together as a package for Purchase
+A Collection represents one or more Albums, Tracks, and/or OtherProducts that are offered together as a package for Purchase
 
 ``` rust
+enum CollectionItem {
+    Album(AlbumId),
+    Track(TrackId),
+    OtherProduct(OtherProductId),
+}
 struct CollectionId {
     id: String,
 }
@@ -390,9 +395,7 @@ struct Collection {
     is_available: bool,
     deleted_by: Option<PersonId>,
     deleted_at: Option<chrono::DateTime>,
-    albums: Option<Vec<Album>>,
-    tracks: Option<Vec<Track>>,
-    other_products: Option<Vec<OtherProduct>>,
+    collection_items: Option<Vec<CollectionMember>>,
 }
 ```
 
@@ -422,7 +425,7 @@ struct OtherProduct {
 
 # Purchase
 
-A Purchase represents one or more Tracks or Albums that a Person purchases from an Artist or Label through the server.
+A Purchase represents one or more Tracks, Albums, Collections, and/or OtherProducts that a Person purchases from an Artist or Label through the server.
 
 ``` rust
 enum PurchaseItemType {
@@ -444,6 +447,7 @@ struct Sku {
     description: Option<String>,
     price: Option<rusty_money::Money>,
     requires_shipping: bool,
+    shipping_charge: Option<rusty_money::Money>,
 }
 struct PurchaseItem {
     id: PurchaseItemId,
@@ -467,6 +471,8 @@ struct Purchase {
     purchased_at: Option<chrono::DateTime>,
     fulfilled_by: Option<Person>,
     fulfilled_at: Option<chrono::DateTime>,
+    coupons_applied: Option<Vec<CouponCodeId>>,
+    total_charge: rusty_money::Money,
 }
 ```