Add missing columns.

librestash/lib/model.py

@@ -75,6 +75,10 @@ class Listing(Base):
     name = Column(String)
     type = Column(String)
 
+    size = Column(String)
+    difficulty = Column(Float)
+    terrain = Column(Float)
+
     summary = Column(String)
     description = Column(String)
     hints = Column(String)