Remove epubfile dependency for python2 support
Remove epubfile dependency for python2 support

Travis CI made it clear that epubfile only supports python 3 or newer.
Since textract claims to still support python2, we have to make sure
the epub parsing solution used here also supports python2.

Since EPUB files are just a collection of HTML documents, and we
already depend on BeautifulSoup which easily parses HTML documents, it
made sense to implement our own EPUB text parser in Python 2 without
any third-party dependencies. The fact that solution is barely 50 lines
long further reinforces the point that a specialized third-party EPUB
parsing library is hardly needed for this task.

deanmalmgren/textract,deanmalmgren/textract,deanmalmgren/textract