Update StripDown for tables

The StripDown renderer handles tables now if tables extension set to true.
Apart from the fact that it adds a spacer between table cells when output, I was thinking of a similiarity with a `.tsv` file. I hadn't actually tried it but I assume it would mean the output could be copy-pasted into a spreadsheet as the table you'd expect. I'll leave it to your judgement though since you know more about the gem and how it all hangs together better than I do.