Added BLEU as eval metric

pom.xml

@@ -18,7 +18,7 @@
 
     <groupId>de.monticore.lang.monticar</groupId>
     <artifactId>cnn-train</artifactId>
-    <version>0.3.7-SNAPSHOT</version>
+    <version>0.3.8-SNAPSHOT</version>
 
     <!-- == PROJECT DEPENDENCIES ============================================= -->
 

src/main/grammars/de/monticore/lang/monticar/CNNTrain.mc4

@@ -36,6 +36,7 @@ grammar CNNTrain extends de.monticore.lang.monticar.Common2, de.monticore.Number
     LossWeightsEntry implements ConfigEntry = name:"loss_weights" ":" value:DoubleVectorValue;
     
     EvalMetricValue implements ConfigValue =(accuracy:"accuracy"
+                                               | bleu:"bleu"
                                                | crossEntropy:"cross_entropy"
                                                | f1:"f1"
                                                | mae:"mae"

src/main/java/de/monticore/lang/monticar/cnntrain/_symboltable/EvalMetric.java

@@ -14,6 +14,12 @@ public enum EvalMetric {
             return "accuracy";
         }
     },
+    BLEU{
+        @Override
+        public String toString() {
+            return "bleu";
+        }
+    },
     CROSS_ENTROPY{
         @Override
         public String toString() {