I walked in the front door of the DoubleTree Hotel Rockville and was greeted not by a member of the hotel, but by the sounds of music... sweet music - horns, piano, drums - and applause. Not every hotel greets its guest this way, except during the East Coast Jazz Festival. Musicians from around the globe are invited to showcase their talents. It's a warm, friendly and very inviting atmosphere. After getting my bearings, and there is a lot to see, everything from the vendors (clothing, paintings,