Fix parsing of tables nested in other block elements

[brson]

The row parser was not scanning from the correct offset.

[kivikakk]

Thank you!

[kivikakk]

I hope this is okay with you — I've added you as a collaborator and marked master as protected, so you can merge yourself after review.

[kivikakk]

In fact, I've revised my decision: feel free to merge without a review first if you're confident. (And this is a pretty clear example of something to be confident about.) I'm a big fan of Peter Hintjens' "optimistic merging" idea.

[brson]

Thanks @kivikakk :)