added $elemMatch query operator support

lib/model.js

@@ -622,7 +622,20 @@ comparisonFunctions.$size = function (obj, value) {
 
     return (obj.length == value);
 };
+comparisonFunctions.$elemMatch = function(obj,value){
+  if (!util.isArray(obj)) { return false; }
+  var i = obj.length;
+  var result = false;   // Initialize result
+  while(i--){
+    if (match(obj[i],value)){   // If match for array element, return true
+      result = true;
+      break;
+    }
+  }
+  return result;
+};
 arrayComparisonFunctions.$size = true;
+arrayComparisonFunctions.$elemMatch = true;
 
 
 /**