Improve tbl support in woman.el.

Improve tbl support in woman.el.

* lisp/woman.el (woman-find-next-control-line): New arg, specifying an
additional regexp component for the control line.
(woman2-roff-buffer): Use it.
(woman-break-table): New function.
(woman2-TS): Use it.

And some cleanups:

* lisp/woman.el (woman-set-buffer-display-table, woman-decode-region)
(woman-horizontal-escapes, woman-negative-vertical-space)
(woman-tab-to-tab-stop, woman2-fc, woman2-TS)
(WoMan-warn-ignored): Use ?\s instead of ?\ .