Add "--continuation" option to "xo" to allow multiple html lines

[philshafer]

See https://lists.freebsd.org/pipermail/freebsd-hackers/2018-September/053304.html

If I choose HTML output I get the following invalid output which is missing
closing tags.

test1

,

2GB

test2

,

4GB

This can be fixed by adding "\n" to the end of the format lines, which may
be required, but it seems strange that I can so easily generate broken
output.

Yes, without a trailing newline, libxo can't declare the output
line "over", so it doesn't make the . The problem is that
there's no mechanism to "xo" that your output line is continued
from the previous one, and since "xo" is stateless, it will happily
start the next chunk of output with a new open div. I'll add a
"--continuation" option.