hanging punctuation for right-aligned blocks?

As part of my research on #52 I also studied whether the push/pull technique could be applied to blocks with `text-align:right` (that is, the punctuation would hang over the right margin instead of the left). I haven’t gotten it to work yet. It may be too complicated to be worthwhile. What I tried:

* In the processor script, closing punctuation would need to be wrapped similar to opening punctuation, though in opposite order: the `pull` would precede the `push`. Also, the wrapping tag for the closing punctuation would want to be distinct from the opening (e.g., `push-open` and `push-closed` rather than just `push`). This part seemed tractable.

* In the CSS, however, I couldn’t come up with a way of styling the `push-closed` and `pull-closed` to get analogous behavior with the usual `push`/`pull` pairs. The usual idea is that in the middle of a line, the two appear together, but at a line break, the `push` remains at the end of one line, the line break happens, and the `pull` appears at the beginning of the next. On the right edge, the `pull` would happen first, at the end of the line, and then assumedly you’d want the `push` to wrap to the next.

* More troublesome still, I couldn’t come up with a way to toggle this behavior purely with CSS. That is, in any given text block, the text is either aligned left or right (or neither) so only the opening push/pull pairs or closing push/pull pairs should work (or neither). But there isn’t any way to write a CSS selector conditioned on the presence of another CSS property. If every right-aligned block was guaranteed to have, say, `class="right"`, then you can have CSS selectors like `.right push-closed` and so on. But that requires the right-alignment to be encoded at “compile time”, rather than strictly in the CSS (where it should be).