Bugfix: fix UTF-8 whitespace detection and provide zero-width detection function

Bugfix: fix UTF-8 whitespace detection and provide zero-width detection function

The whitespace detection codes for UTF-8 were incorrect.

Non-printing characters, called zero-width, are not whitespace.
Move them out of the whitespace detection and provide a new function for detecting zero-width.

Handle additional UTF-8 whitespace character codes that I had previously missed.