doc/: Align layout control commands to right margin in `tabbing' etc.

doc/: Align layout control commands to right margin in `tabbing' etc.

This is mostly clean in `--word-diff'.  Here are the exceptions.

  * doc/parsing.tex: `--word-diff' gets confused around the various
    `condition-with-location' subclasses.  This is clean in `-b', so
    there's not actually anything complicated happening here.

  * doc/parsing.tex: I've sneakily removed a pointless trailing `%'.

  * doc/runtime.tex: I've inserted a couple of linebreaks with `%' so as
    to shorten the source-file lines.

  * doc/runtime.tex: Some `\-' have harmlessly moved past `@\\' macro-
    backslashes to take their proper places on the right margin.