Hundreds of Muslims gathered in Roxbury yesterday to celebrate the religious holiday Eid al-Fitr, which marks the end of Ramadan’s month-long holy fast.The Islamic Society of Boston Cultural Center’s Imam Skaykh Yasir Fahmy and Director Yusufi Vali joined the crowd in kneeling behind the Madison Park Technical Vocational High School in celebration of the breaking of the Ramadan fast.Mayor Martin J.