manual: Update book example
* examples/johnw/muse-johnw.el: Update for preferred muse-derive-style
usage. Rename to muse-init.el.
* examples/mwolson/muse-init.el: Update.
* lisp/muse-book.el (muse-book-publish-p): New function split from
muse-book-publish.
(muse-book-get-directives): New function that retrieves the publishing
directives from the given file.
(muse-book-publish): Use muse-book-get-directives to set the title if
no title was specified.
* texi/muse.texi (Book): Mention new way to publish books and provide an
example, since the process may be non-obvious.
git-archimport-id: mwolson@gnu.org--2006/muse--main--1.0--patch-259