A southern Illinois airport that has struggled to attract commercial service since opening nearly two decades ago is adding twice-weekly service to southwest Florida.  Mid America Airport announced Thursday that low-cost Allegiant Air will offer twice-weekly trips to Punta Gorda, Florida starting February 18th.  Allegiant also flies from Mid America to Saint Petersburg and Sanford, Florida.  A Las Vegas route began earlier this month.  Airport owner Saint Clair County lost more than $6 million in 2013 on Mid America and has yet to turn a profit since its 1997 opening.  That figure climbed to nearly $13 million counting depreciation.