Identify time uncertainty for "etwa"

Close #37

src/NodaTimeSplitter.php

@@ -98,6 +98,7 @@ final class NodaTimeSplitter {
         ", ",
         " und ",
         "nach ",
+        "nach dem ",
         "um ",
         "ca.",
         "ab ",
@@ -831,6 +832,15 @@ final class NodaTimeSplitter {
             }
         }
 
+        if (\preg_match("/^(Nach dem|nach dem)\ /", $datum)) {
+            if (($spacePos = \strpos($datum, " ", 6)) === false) {
+                return false;
+            }
+            if ($output = self::attempt_splitting(\substr($datum, $spacePos))) {
+                return self::_turn_noda_split_time_to_after($output);
+            }
+        }
+
         if (\preg_match("/\ (\(nach|nach)$/", $datum)) {
             if (($spacePos = \strpos($datum, " ")) === false) {
                 return false;

src/NodaUncertaintyHelper.php

@@ -107,6 +107,8 @@ final class NodaUncertaintyHelper {
         "za. ",
         "~",
         "circa ",
+        "etwa ",
+        "Etwa ",
         "gegen ",
         "um ",
         "Um ",