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/README.md

@@ -0,0 +1,72 @@
+This is an example application that is using the Qtk API to create custom Qt
+OpenGL widgets. This is very similar to `QtkWidget` in the Qtk desktop
+application source code, but could be modified for different uses if needed.
+
+There are no camera controls supported in this example. The camera is fixed.
+If these controls are desired, they can be implemented by the client.
+
+You can import your own models within `examplescene.cpp`, inside the
+`ExampleScene::init()` function. Rotations and translations
+are applied in `ExampleScene::update()`.
+
+The syntax for adding shapes and models is seen in the example below.
+This would result in a scene with a red cube and a miniature spartan model
+placed on top.
+
+```C++
+void ExampleScene::init() {
+  // Add a skybox to the scene using default cube map images and settings.
+  setSkybox(new Qtk::Skybox("Skybox"));
+
+  /* Create a red cube with a mini master chief on top. */
+  auto myCube = new MeshRenderer("My cube", Cube(Qtk::QTK_DRAW_ELEMENTS));
+  myCube->setColor(RED);
+  mMeshes.push_back(myCube);
+
+  auto mySpartan = new Model("My spartan", "/path/to/spartan/spartan.obj");
+  mySpartan->getTransform().setTranslation(0.0f, 0.5f, 0.0f);
+  mySpartan->getTransform().setScale(0.5f);
+  mModels.push_back(mySpartan);
+}
+```
+
+If we want to make our spartan spin, we need to apply rotation in `update`
+
+```C++
+void ExampleScene::update() {
+  auto mySpartan = Model::getInstance("My spartan");
+  mySpartan->getTransform().rotate(0.75f, 0.0f, 1.0f, 0.0f);
+
+  auto myCube = MeshRenderer::getInstance("My cube");
+  myCube->getTransform().rotate(-0.75f, 0.0f, 1.0f, 0.0f);
+}
+```
+
+Other examples can be found in the source files for this example project.
+
+## Build Instructions
+
+Currently, this application requires manual build and installation of Qtk.
+In the future, once a release is published, I will be able to use `FetchContent`
+or similar cmake functionality to remove this requirement.
+
+For Qtk build instructions, see the README in the root of this repository.
+
+```bash
+cmake -S /path/to/qtk/example-app/ -B /path/to/qtk/example-app/build
+cmake --build /path/to/qtk/example-app/build
+```
+
+If Qtk was not installed system-wide, we can set `QTK_PATH` to point to the
+custom installation directory.
+
+```bash
+cmake -S /path/to/qtk/example-app/ -B /path/to/qtk/example-app/build -DQTK_PATH=/path/to/qtk/install/
+cmake --build /path/to/qtk/example-app/build
+```
+
+After this, we can run the example application -
+
+```bash
+./path/to/qtk/example-app/build/bin/example
+```