[pep8] PEP8 changes for create_isbn_edition.py

• Code style issues
• clear trailing white space
• untabify file
• keep lines below 80 chars
• update function documentation and parameter list
• update shebang
• script documentation is in doc
• replace print statements by pywikibot.info
• add main() function, mostly needed for windows and for script tests
• add pywikibot.handle_args to handle global options and test -help
• add isbnlib dependency
• lazy import isbnlib and unidecode
• replace sys.stdin.read by pywikibot.input to show a input message
• create wikidata_site and repo after global args are read to prevent site warning

Change-Id: I6917ec9b511db609c2f1828486b9a53998d1e376