Provide a cleanup function for the term_tab module, freeing memory
and resetting the internal state to the initial state.
Call this function from the proper place in term_free().

With the way the module is currently used, this does not imply any
functional change, but doing proper cleanup is more robust, makes
it easier during code review to understand what is going on, and
makes it explicit that there is no memory leak.

tables leak tab settings to subsequent text

improve rounding rules for scaling units
in horizontal orientation in the terminal formatter

make the internal a2roffsu() interface more powerful by returning
a pointer to the end of the parsed data, making it easier to
parse subsequent bytes

Basic implementation of the roff(7) .ta (define tab stops) request.
This is the first feature made possible by the parser reorganization.
Improves the formatting of the SYNOPSIS in many Xenocara GL manuals.
Also important for ports, as reported by many, including naddy@.

tables leak tab settings to subsequent text

improve rounding rules for scaling units
in horizontal orientation in the terminal formatter

make the internal a2roffsu() interface more powerful by returning
a pointer to the end of the parsed data, making it easier to
parse subsequent bytes

Basic implementation of the roff(7) .ta (define tab stops) request.
This is the first feature made possible by the parser reorganization.
Improves the formatting of the SYNOPSIS in many Xenocara GL manuals.
Also important for ports, as reported by many, including naddy@.