1. The QWinRegistryKey class was introduced in 5.14.0. The implementation is quite clean, so just copy the sources files from Qt repo in case the user is linking against a version older than 5.14.
2. Fixes the rounding error of the self-painted frame border of the examples.
3. Other minor tweaks.
Fixes: #95
Task-number: #94
Signed-off-by: Yuhang Zhao <2546789017@qq.com>