WinTab support for Qt 5.x

Few people know that WinTab support has gone for a while since Qt 5.0. The reason is complicated, you can check maillist of Qt developers if you interested.

Here I wrote a homemade support for it, basically just wrap the API myself. But it works!

https://github.com/liuyanghejerry/Qt-TabletSupport

Also, feel free to make pull requests.