parse-wormedit: level rendering

parse-wormedit: level rendering

If --render is given, outputs an approximate drawing of all singleplayer
levels.  The result is not an exact representation: slopes may be drawn
slightly differently because Imager::Draw is used for simplicity.

To write directly to a file, --output can be given.  Its file name
extension determines the format (.txt and .yaml for default and raw
output, anything else will be parsed by Imager::Files, which supports
most common image types).