allow classes in any order on p elements
allow classes in any order on p elements

fixes #139

mtmse/nordic-epub3-dtbook-migrator,mtmse/nordic-epub3-dtbook-migrator,mtmse/nordic-epub3-dtbook-migrator,nlbdev/nordic-epub3-dtbook-migrator,nlbdev/nordic-epub3-dtbook-migrator,nlbdev/nordic-epub3-dtbook-migrator,nlbdev/nordic-epub3-dtbook-migrator,mtmse/nordic-epub3-dtbook-migrator