Terance Mathis, sporting a Pinecrest Academy polo and a grin that was on more than it was off, surveyed the crowded gym and snapped a few selfies. As he took questions from parents, he swayed back and forth in his chair, his excitement turning into motion. Mathis, a former Pro Bowl receiver with the Atlanta Falcons, was introduced as Pinecrest’s new head football coach on Friday, capping a rapid coaching search that began last week, when Todd Winter resigned to take the job at Holy Innocents.