By Wilton Jackson The track and field star is running for more than medals in her final season. Allyson Felix, one of the greatest track and field athletes in U.S. history, will hang up her cleats after this season. The 36-year-old announced her retirement in a heartfelt note Wednesday on Instagram, thanking those who have supported her in career that she never in her “wildest dreams” imagined. “As a little girl they called chicken legs… I have so much gratitude for this sport that has changed my life,” Felix wrote. I have given everything I have to running and for the first time I’m not sur…