[Feature] Models of the service (#1)

This PR contains the implementation of all the models used by this service: `Amiibo`, `Amiibo.Game`, `Amiibo.Release`, `Amiibo.Usage`, `KeyName` and `LastUpdated`.

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: #1

Sources/Models/Amiibo.swift

@@ -0,0 +1,18 @@
+public struct Amiibo {
+    public let type: String
+    public let head: String
+    public let tail: String
+    public let name: String
+    public let character: String
+    public let amiiboSeries: String
+    public let gameSeries: String
+    public let image: String
+    public let release: Release
+    public let games3DS: [Game]?
+    public let gamesWiiU: [Game]?
+    public let gamesSwitch: [Game]?
+}
+
+// MARK: - Decodable
+
+extension Amiibo: Decodable {}

Sources/Models/AmiiboGame.swift

@@ -0,0 +1,17 @@
+extension Amiibo {
+    public struct Game {
+        public let identifiers: [String]
+        public let name: String
+        public let usage: [Usage]
+    }
+}
+
+// MARK: - Decodable
+
+extension Amiibo.Game: Decodable {
+    enum CodingKeys: String, CodingKey {
+        case identifiers = "gameID"
+        case name = "gameName"
+        case usage = "amiiboUsage"
+    }
+}

Sources/Models/AmiiboRelease.swift

@@ -0,0 +1,21 @@
+import Foundation
+
+extension Amiibo {
+    public struct Release {
+        public let australia: Date?
+        public let europe: Date?
+        public let japan: Date?
+        public let america: Date?
+    }
+}
+
+// MARK: - Decodable
+
+extension Amiibo.Release: Decodable {
+    enum CodingKeys: String, CodingKey {
+        case australia = "au"
+        case europe = "eu"
+        case japan = "jp"
+        case america = "na"
+    }
+}

Sources/Models/AmiiboUsage.swift

@@ -0,0 +1,15 @@
+extension Amiibo {
+    public struct Usage {
+        public let explanation: String
+        public let isWritable: Bool
+    }
+}
+
+// MARK: - Decodable
+
+extension Amiibo.Usage: Decodable {
+    enum CodingKeys: String, CodingKey {
+        case explanation = "Usage"
+        case isWritable = "write"
+    }
+}

Sources/Models/KeyName.swift

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+public struct KeyName {
+    public let key: String
+    public let name: String?
+}
+
+// MARK: - Decodable
+
+extension KeyName: Decodable {}
+
+// MARK: - Type aliases
+
+public typealias AmiiboType = KeyName
+public typealias AmiiboSeries = KeyName
+public typealias GameSeries = KeyName
+public typealias Character = KeyName

Sources/Models/LastUpdated.swift

@@ -0,0 +1,13 @@
+import Foundation
+
+public struct LastUpdated {
+    public let timestamp: Date
+}
+
+// MARK: - Decodable
+
+extension LastUpdated: Decodable {
+    enum CodingKeys: String, CodingKey {
+        case timestamp = "lastUpdated"
+    }
+}