Create nfl_pbp_update.xlsm

Excel macro that adds columns Play Type and Net Gain to play by play data (obtained from http://www.advancednflstats.com/2010/04/play-by-play-data.html) also creates new tables for game (home, away, final score) and drive results (home, away, current score, n_plays, starting ydline, net_yards, drive result, n_points, etc)