Well, I was just thinking about #159 today and figured that would require eliminating `/` from goodchars. Of course I would like to make goodchars as restrictive as possible, but I wasn't sure what would break if I added more constraints... Still, yes, both `%` and `/` seem reasonable to eliminate. 

(FYI, that regexp is a cut-down version of the PEG parser for JSON strings, stolen from here: https://github.com/dmajda/pegjs/blob/master/examples/json.pegjs#L58)