[SwiftPM] Use V4 PackageDescription

Package.resolved

@@ -0,0 +1,16 @@
+{
+  "object": {
+    "pins": [
+      {
+        "package": "Result",
+        "repositoryURL": "https://github.com/antitypical/Result.git",
+        "state": {
+          "branch": null,
+          "revision": "7477584259bfce2560a19e06ad9f71db441fff11",
+          "version": "3.2.4"
+        }
+      }
+    ]
+  },
+  "version": 1
+}

Package.swift

@@ -1,9 +1,24 @@
+// swift-tools-version:4.0
 import PackageDescription
 
 let package = Package(
     name: "APIKit",
+    products: [
+        .library(name: "APIKit", targets: ["APIKit"]),
+    ],
     dependencies: [
-        .Package(url: "https://github.com/antitypical/Result.git", majorVersion: 3),
+        .package(url: "https://github.com/antitypical/Result.git", from: "3.0.0"),
+    ],
+    targets: [
+        .target(
+            name: "APIKit", 
+            dependencies: ["Result"],
+            exclude: ["BodyParameters/AbstractInputStream.m"]
+        ),
+         .testTarget(
+            name: "APIKitTests",
+            dependencies: ["APIKit"]
+        ),
     ],
-    exclude: ["Sources/APIKit/BodyParameters/AbstractInputStream.m"]
+    swiftLanguageVersions: [4]
 )