This returns a label handle which allows you to remove, reposition, or replace the label later.
In addition to all the features of wesnoth.print, you can now specify where the label appears onscreen, as well as a fadeout time separate from the duration.
You can also anchor the text to an edge or corner instead of centering in on the screen,
specify the maximum width it can occupy as an absolute width or a percentage,
and specify a background colour and transparency.
It includes a demo scenario that demonstrates many of the capabilities of the API.
To play the demo scenario, run with -toverlay_text_demo or select it from the in-game test list.
