Work on running tinyjs; modified bin_item rules.

A bin_item rule, which I might rename later, is a rule item that starts with
an equal sign. I used to allow these to be code blocks, but then I thought it
made more sense to only allow one-line code pieces there. I could reconsider.
However, for now this fixes a bug where an indented code block would be
misinterpreted as a return None followed by unexecuted code.