Continued adding "--skeleton" switch.

Continued adding "--skeleton" switch.

Moved input-string-generation-from-DFA algorithm earlier, to the
point when DFA is barely constructed and contains only 'Match'
states and starting state (no saving, accepting or split states).
This simplifies string generation: if destination state is NULL,
it is either next to final state (if all spans lead to it), or
default state (if some spans lead to other states).