Documentation/user/programming-interface.itely: fix @{ @}.

Documentation/user/programming-interface.itely: fix @{ @}.
scm/define-markup-commands.scm: add linewidth info to
\justify and \wordwrap.
Documentation/user/advanced-notation.itely: shaped->shape
lily/note-heads-engraver.cc: changed Shaped->Shape in a
comment.  No actual code was touched.
Documentation/user/invoking.itely: add more info about
\include.  Thanks, Bruce!