add MultiIndex class

meteoinfo-dataframe/src/main/java/org/meteoinfo/dataframe/Index.java

@@ -123,6 +123,8 @@ public class Index<V> implements Iterable<V>{
             return new IntIndex(data);
         } else if (data.get(0) instanceof String) {
             return new StringIndex(data);
+        } else if (data.get(0) instanceof List) {
+            return new MultiIndex(data);
         } else {
             return null;
         }

meteoinfo-dataframe/src/main/java/org/meteoinfo/dataframe/MultiIndex.java

@@ -0,0 +1,13 @@
+package org.meteoinfo.dataframe;
+
+import java.util.List;
+
+public class MultiIndex extends Index<List> {
+    /**
+     * Construction
+     * @param data The index data
+     */
+    public MultiIndex(List data) {
+        this.data = data;
+    }
+}