create-html-usage.pl: unwrap multi-line usage lines
The .rst formatter does its own wrapping (and so does the browser).
Therefore unwrap single-command usage lines that were manually
wrapped onto multiple lines for easier reading of the terminal
output.
The "Or:" alternatives were already being handled just so long as
they (and the preceding Usage:) were each one single line.
Now folding those "logical" lines is allowed and they will then
be unfolded when creating the .rst usage information.
Until just recently there was no need for unfolding support.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>