Time splitter: Handle first/second half

Close #31

src/NodaTimeSplitter.php

@@ -1101,6 +1101,15 @@ final class NodaTimeSplitter {
 
         if (empty($datum)) return '';
 
+        if (\preg_match("/^1\.\ (Halbjahr|Hälfte)\ [0-9]{4}$/", $datum)) {
+            $year = substr($datum, -4);
+            return "Januar $year-Juni $year";
+        }
+        if (\preg_match("/^2\.\ (Halbjahr|Hälfte)\ [0-9]{4}$/", $datum)) {
+            $year = substr($datum, -4);
+            return "Juli $year-Dezember $year";
+        }
+
         $inputLength = strlen($datum);
 
         // Hungarian year and month until month