Add support for Swift Package Manager

Package.swift

@@ -0,0 +1,52 @@
+// swift-tools-version:5.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "SDWebImage",
+    platforms: [
+        .macOS(.v10_10),
+        .iOS(.v8),
+        .tvOS(.v9),
+        .watchOS(.v2)
+    ],
+    products: [
+        // Products define the executables and libraries produced by a package, and make them visible to other packages.
+        .library(
+            name: "SDWebImage",
+            targets: ["SDWebImage"]),
+        .library(
+            name: "SDWebImageMapKit",
+            targets: ["SDWebImageMapKit"])
+    ],
+    dependencies: [
+        // Dependencies declare other packages that this package depends on.
+        // .package(url: /* package url */, from: "1.0.0"),
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
+        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
+        .target(
+            name: "SDWebImage",
+            dependencies: [],
+            path: "SDWebImage",
+            exclude: ["Private", "MapKit"],
+            cSettings: [
+                .headerSearchPath("."),
+                .headerSearchPath("Private")
+            ]
+        ),
+        .target(
+            name: "SDWebImageMapKit",
+            dependencies: ["SDWebImage"],
+            path: "SDWebImage",
+            sources: ["MapKit/MKAnnotationView+WebCache.h", "MapKit/MKAnnotationView+WebCache.m"],
+            publicHeadersPath: "MapKit",
+            cSettings: [
+                .headerSearchPath("."),
+                .headerSearchPath("Private")
+            ]
+        )
+    ]
+)