Add straighten way operation and action

data/core.yaml

@@ -63,6 +63,13 @@ en:
         line: Squared the corners of a line.
         area: Squared the corners of an area.
       not_closed: This can't be made square because it's not a loop.
+    straighten:
+      title: Straighten
+      description: Straighten this line.
+      key: S
+      annotation: Straightened the line.
+      is_closed: This can't be straightened because it's a loop.
+      too_bendy: This can't be straightened because it's too bendy.
     delete:
       title: Delete
       description: Remove this from the map.