Add Swift Package Manager support (#501)

.gitignore

@@ -1,3 +1,4 @@
+.build/
 project.xcworkspace
 xcuserdata
 Examples/

Package.swift

@@ -1,3 +1,4 @@
+// swift-tools-version:4.0
 //
 //  SnapKit
 //
@@ -25,5 +26,12 @@
 import PackageDescription
 
 let package = Package(
-    name: "SnapKit"
+    name: "SnapKit",
+    products: [
+        .library(name: "SnapKit", targets: ["SnapKit"]),
+    ],
+    targets: [
+        .target(name: "SnapKit", path: "Source"),
+        .testTarget(name: "SnapKitTests", dependencies: ["SnapKit"]),
+    ]
 )

SnapKit.xcodeproj/project.pbxproj

@@ -82,8 +82,8 @@
 		EEBCC9E219CC627E0083B827 /* SnapKit Tests.xctest */ = {isa = PBXFileReference; explicitFileType = wrapper.cfbundle; includeInIndex = 0; path = "SnapKit Tests.xctest"; sourceTree = BUILT_PRODUCTS_DIR; };
 		EECDB3641AC0C95C006BBC11 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
 		EECDB3661AC0C95C006BBC11 /* SnapKit.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = SnapKit.h; sourceTree = "<group>"; };
-		EECDB3691AC0C95C006BBC11 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
-		EECDB36A1AC0C95C006BBC11 /* Tests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Tests.swift; sourceTree = "<group>"; };
+		EECDB3691AC0C95C006BBC11 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; name = Info.plist; path = SnapKitTests/Info.plist; sourceTree = "<group>"; };
+		EECDB36A1AC0C95C006BBC11 /* Tests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; name = Tests.swift; path = SnapKitTests/Tests.swift; sourceTree = "<group>"; };
 		EEF68F9D1D78492400980C26 /* ConstraintLayoutGuideDSL.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ConstraintLayoutGuideDSL.swift; sourceTree = "<group>"; };
 		EEF68FA51D784A5300980C26 /* ConstraintDSL.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = ConstraintDSL.swift; sourceTree = "<group>"; };
 		EEF68FAF1D784FB100980C26 /* ConstraintLayoutGuide+Extensions.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "ConstraintLayoutGuide+Extensions.swift"; sourceTree = "<group>"; };
@@ -559,7 +559,7 @@
 			buildSettings = {
 				"CODE_SIGN_IDENTITY[sdk=iphoneos*]" = "iPhone Developer";
 				DEVELOPMENT_TEAM = "";
-				INFOPLIST_FILE = "$(SRCROOT)/Tests/Info.plist";
+				INFOPLIST_FILE = "$(SRCROOT)/Tests/SnapKitTests/Info.plist";
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks @loader_path/../Frameworks @executable_path/../Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = "io.snapkit.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
@@ -572,7 +572,7 @@
 			buildSettings = {
 				"CODE_SIGN_IDENTITY[sdk=iphoneos*]" = "iPhone Developer";
 				DEVELOPMENT_TEAM = "";
-				INFOPLIST_FILE = "$(SRCROOT)/Tests/Info.plist";
+				INFOPLIST_FILE = "$(SRCROOT)/Tests/SnapKitTests/Info.plist";
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks @loader_path/../Frameworks @executable_path/../Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = "io.snapkit.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";