CI: 32-bit GCC/MSYS2 build for Windows (#15405)

Fix the outdated post url

CI: Building on Windows (with MSYS2) using GCC and Clang (#15405)

Use clang-format 6.0 to check for code style (#15403, #15404)

GitHub Actions: split the workflows (#15403)

GitHub Actions: split the workflows (#15403)

Switch CI to Github Actions (#15403)

docs: Fix simple typo, wihout -> without

Replace NULL (or 0) with Q_NULLPTR

Remove QSsl deprecation warnings

Remove OS2 icons and resources

Remove QString::null deprecation warnings

Initialize progress right away with QtWebKit 5.212 (#15342)

Remove astyle completely

CI to check for coding style (#15404)