This adds an option to enable white spece detection, and two
further options to control the operation of white space detection.

White space detection (--print-spaces) is intended for use cases
where digit (resp. character) grouping is important for correct
interpretation.  One use case is the recognition of superimposed
dates in photographic images.

This commit also increases the version number to 2.21.0 and tweaks
some debug output.