refactor: aliasing logic to addRels

* also shorten query builder alias logic

src/PostgREST/Plan/ReadPlan.hs

@@ -43,6 +43,9 @@ data ReadPlan = ReadPlan
   , relHint      :: Maybe Hint
   , relJoinType  :: Maybe JoinType
   , depth        :: Depth
+  -- depth is used bc when a self join occurs we
+  -- need to differentiate the parent from the child tables by having an alias like
+  -- "table_depth". See http://github.com/PostgREST/postgrest/issues/987.
   }
   deriving (Eq)