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Fix issue #336
epubcheck.sh shell script fixed.
Merge pull request #338 from skreutzer/master

epubcheck.sh shell script fixed. Also fixes #321.
fixed typo in media overlay audio error message // issue #350
B&N's contribution
line endings
fixup tests after merging the main branch into this
update readme.md, README-dist.txt
fix one more failing test that shouldn't have gotten in that way.
ACC_007 & ACC_008 should only be raised on Epub3, not on Epub2.
Fixed a null reference exception when a spine item refers to a non-existent manifest item.  The execption is caught, but zero error messages are reported.
fix merge conflict and make sure the tests pass.
fixup merge