chore: prepare release v4.2.0
chore: prepare release v4.2.0

IDPF/epubcheck,mihailim/epubcheck,mihailim/epubcheck,IDPF/epubcheck,IDPF/epubcheck,w3c/epubcheck,IDPF/epubcheck,w3c/epubcheck,mihailim/epubcheck,IDPF/epubcheck,mihailim/epubcheck,mihailim/epubcheck,w3c/epubcheck