Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Extensions/Foundation/Package.swift

@@ -0,0 +1,23 @@
+import PackageDescription
+
+let package = Package(
+    name: "PMKFoundation",
+    dependencies: [
+        .Package(url: "https://github.com/mxcl/PromiseKit.git", majorVersion: 6)
+    ],
+    swiftLanguageVersions: [3, 4],
+    exclude: [
+        "Sources/NSNotificationCenter+AnyPromise.m",
+        "Sources/NSTask+AnyPromise.m",
+        "Sources/NSURLSession+AnyPromise.m",
+        "Sources/PMKFoundation.h",
+		"Tests"  // currently SwiftPM is not savvy to having a single test…
+    ]
+)
+
+#if os(Linux)
+package.exclude += [
+    "Sources/afterlife.swift",
+    "Sources/NSObject+Promise.swift"
+]
+#endif