Improve user field declarations

Sources/App/Model/User.swift

@@ -1,7 +1,18 @@
 import FluentSQLiteDriver
+import FluentSQL
 import Vapor
 
+private extension FieldProperty {
+    convenience init(_ key: User.Key) {
+        self.init(key: key.key)
+    }
+}
 
+private extension OptionalParentProperty {
+    convenience init(_ key: User.Key) {
+        self.init(key: key.key)
+    }
+}
 
 /// A registered user
 final class User: Model {
@@ -26,19 +37,19 @@ final class User: Model {
     var id: UUID?
 
     /// The user's full name.
-    @Field(key: Key.name.key)
+    @Field(.name)
     var name: String
 
     /// The hash of the user's password
-    @Field(key: Key.hash.key)
+    @Field(.hash)
     var passwordHash: String
 
     /// The user's total points
-    @Field(key: Key.points.key)
+    @Field(.points)
     var points: Int
 
-    // Example of an optional parent relation.
+    /// The table to which this user currently belongs
-    @OptionalParent(key: Key.table.key)
+    @OptionalParent(.table)
     var table: Table?
 
     init() { }