Fixed WindowMode

- Made FullScreen wrap a borrowed Monitor.
- Removed from_ptr
- Changed ‘get_window_mode’ to take a closure.
Renamed get methods that take closures

- get_primary_monitor -> with_primary_monitor
- get_connected_monitors -> with_connected_monitors
- get_window_mode -> with_window_mode

Updated examples too.
Merge pull request #141 from bvssvni/windowmode-fix

Fixed WindowMode