Improve cmake and GUI (#13)

+ Packaging and CI for Windows, Mac, Linux
+ Debian package, NSIS Windows installer, OSX appbundle
+ Example application using libqtk
+ Component installation for `qtk`, `libqtk`, or `collection` with cmake

example-app/examplewidget.cpp

@@ -0,0 +1,57 @@
+/*##############################################################################
+## Author: Shaun Reed                                                         ##
+## Legal: All Content (c) 2023 Shaun Reed, all rights reserved                ##
+## About: Example Qtk widget                                                  ##
+##                                                                            ##
+## Contact: shaunrd0@gmail.com  | URL: www.shaunreed.com | GitHub: shaunrd0   ##
+##############################################################################*/
+
+#include <qtk/scene.h>
+
+#include "examplewidget.h"
+
+ExampleWidget::ExampleWidget(QWidget * parent) :
+    QOpenGLWidget(parent), mScene(new ExampleScene(new Qtk::SceneEmpty)) {
+  // NOTE: The decorator pattern is used to save / load scenes in Qtk currently.
+  // The initializer above sets mScene to the concrete decorator ExampleScene.
+  // Qtk::SceneEmpty provides an empty scene as the concrete component.
+  // ExampleScene is defined in client source, deriving Qtk::SceneInterface.
+
+  QSurfaceFormat format;
+  format.setRenderableType(QSurfaceFormat::OpenGL);
+  format.setProfile(QSurfaceFormat::CoreProfile);
+  format.setVersion(4, 6);
+  format.setSamples(4);
+  format.setDepthBufferSize(16);
+  setFormat(format);
+  setFocusPolicy(Qt::ClickFocus);
+}
+
+void ExampleWidget::initializeGL() {
+  initializeOpenGLFunctions();
+  connect(this, SIGNAL(frameSwapped()), this, SLOT(update()));
+  glEnable(GL_MULTISAMPLE);
+  glEnable(GL_DEPTH_TEST);
+  glDepthMask(GL_TRUE);
+  glDepthFunc(GL_LEQUAL);
+  glDepthRange(0.1f, 1.0f);
+  glClearDepth(1.0f);
+  glClearColor(0.0f, 0.25f, 0.0f, 0.0f);
+  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+}
+
+void ExampleWidget::resizeGL(int width, int height) {
+  Qtk::Scene::getProjectionMatrix().setToIdentity();
+  Qtk::Scene::getProjectionMatrix().perspective(
+      45.0f, float(width) / float(height), 0.1f, 1000.0f);
+}
+
+void ExampleWidget::paintGL() {
+  glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
+  mScene->draw();
+}
+
+void ExampleWidget::update() {
+  mScene->update();
+  QWidget::update();
+}