- Let window type detection start with the client window if there's one,
in hope to enhance performance.
- Change get_wintype_prop() to fetch the property only once.
- Default to WINTYPE_UNKNOWN instead of WINTYPE_NORMAL if
_NET_WM_WINDOW_TYPE is missing.
- Fix a mistake in calc_opacity().
- Add some items to .gitignore.
- Fix a typo in usage().