Deprecate '.' for disambiguating resource embedding

'+' should be used instead.

src/PostgREST/Parsers.hs

@@ -124,7 +124,10 @@ pRelationSelect :: Parser SelectItem
 pRelationSelect = lexeme $ try ( do
     alias <- optionMaybe ( try(pFieldName <* aliasSeparator) )
     fld <- pField
-    relationDetail <- optionMaybe ( try( char '.' *> pFieldName ) )
+    relationDetail <- optionMaybe (
+        try ( char '+' *> pFieldName ) <|>
+        try ( char '.' *> pFieldName ) -- TODO deprecated, remove in next major version
+      )
 
     return (fld, Nothing, alias, relationDetail)
   )