Allow option for rewrapping captions

[okrick]

Enhancement request.

Currently we have to put '' at the end of lines for multiple line captions if we want them to rewrap. Not allowing caption rewrapping produces odd results when an image is viewed on a small screen.

My preference would be to rewrap captions as a default and use out of line markup for bundles of lines that should not be rewrapped, such as ".nf" no-fill blocks.

An alternative would be to add an option to the .il command such as "wrap=yes".

The current process can get intense when there are hundreds of images with multi-line captions.