Lock publick methods to prevent concurrency issues

CHANGELOG.md

@@ -1,5 +1,10 @@
 # KeychainSwift version history
 
+## 16.0.0 (2019-05-28)
+
+Made all methods (get, set, delete and clear) thread-safe to prevent crashing when called from different threads.
+
+
 ## 15.0.0 (2019-04-24)
 
 Added ability to return data as reference ([mediym41](https://github.com/mediym41)).

KeychainSwift.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name        = "KeychainSwift"
-  s.version     = "15.0.0"
+  s.version     = "16.0.0"
   s.license     = { :type => "MIT" }
   s.homepage    = "https://github.com/evgenyneu/keychain-swift"
   s.summary     = "A library for saving text and data in the Keychain with Swift."

README.md

@@ -36,7 +36,7 @@ Simply add [KeychainSwiftDistrib.swift](https://github.com/evgenyneu/keychain-sw
 
 #### Setup with Carthage (iOS 8+)
 
-Alternatively, add `github "evgenyneu/keychain-swift" ~> 15.0` to your Cartfile and run `carthage update`.
+Alternatively, add `github "evgenyneu/keychain-swift" ~> 16.0` to your Cartfile and run `carthage update`.
 
 #### Setup with CocoaPods (iOS 8+)
 
@@ -44,7 +44,7 @@ If you are using CocoaPods add this text to your Podfile and run `pod install`.
 
     use_frameworks!
     target 'Your target name'
-    pod 'KeychainSwift', '~> 15.0'
+    pod 'KeychainSwift', '~> 16.0'
 
 
 #### Setup with Swift Package Manager
@@ -58,7 +58,7 @@ import PackageDescription
 let package = Package(
     name: "MyApp",
     dependencies: [
-        .package(url: "https://github.com/evgenyneu/keychain-swift.git", from: "15.0.0")
+        .package(url: "https://github.com/evgenyneu/keychain-swift.git", from: "16.0.0")
     ],
     targets: [
         .target(