Doc: correct the format of Q_PLUGIN_METADATA macro in sample codes

Change-Id: I464a0c0a590b0b90cf0fe7ccd448ee9bf704bd4f
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Support hotplugging of input devices with XInput2

Since we only scan for XInput2 devices on application start, we will
currently miss any devices plugged in while the application is running.

This patch makes QXcbConnection listen for XInput2 hierachyChanged
events and use them to trigger a rescan of XInput2 devices.

This fixes a regression in Qt 5.3, where the scroll wheel on hot-
plugged mice does not work until the Qt application is restarted.

Change-Id: I2cdc7ca24d3ab00716cedc4b22355b6e4935b184
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>