Mark UIKit extensions as @objc (#42)

* Mark UIKit extensions as @objc

* Create CHANGELOG.md

Author: klaaspieter

CHANGELOG.md

@@ -0,0 +1,3 @@
+# [Unreleased](https://github.com/seedco/StackViewController/compare/0.4.0...HEAD)
+
+- Fix runtime crashes (unrecognized selector) by adding `@objc` annotation to public UIKit extensions. 

StackViewController/UIStackViewExtensions.swift

@@ -8,8 +8,8 @@
 
 import UIKit
 
-extension UIStackView {
-    public func removeAllArrangedSubviews() {
+public extension UIStackView {
+    @objc public func removeAllArrangedSubviews() {
         arrangedSubviews.forEach {
             $0.removeFromSuperview()
         }

StackViewController/UIViewExtensions.swift

@@ -8,8 +8,8 @@
 
 import UIKit
 
-extension UIView {
-    public func activateSuperviewHuggingConstraints(insets: UIEdgeInsets = UIEdgeInsets.zero) -> [NSLayoutConstraint] {
+public extension UIView {
+    @objc public func activateSuperviewHuggingConstraints(insets: UIEdgeInsets = UIEdgeInsets.zero) -> [NSLayoutConstraint] {
         translatesAutoresizingMaskIntoConstraints = false
         let views = ["view": self]
         let metrics = ["top": insets.top, "left": insets.left, "bottom": insets.bottom, "right": insets.right]