Update SegmentBuilder.java

Add att() method for StreamBuilder API

Author: bigloupe

src/org/beanio/builder/SegmentBuilder.java

@@ -41,6 +41,16 @@ protected SegmentBuilder me() {
         return this;
     }
 
+    /**
+     * Sets the position of the field.
+     * @param at the position
+     * @return this
+     */
+    public SegmentBuilder at(int at) {
+        config.setPosition(at);
+        return this;
+    }
+    
     /**
      * Indicates the number of occurrences of this segment is governed by another field.
      * @param ref the name of the field that governs the occurrences of this segment