update sample Rakefile; add targets pdf, epub and clean
update sample Rakefile; add targets pdf, epub and clean

kuad9/review_study,orangain/review,takahashim/review,murashitas/review,suzuki/review,kmuto/review,krororo/review,orangain/review,takahashim/review,masawada/review,krororo/review,masawada/review,krororo/review,kmuto/review,suzuki/review,kmuto/review,murashitas/review,kuad9/review_study