Credentials
Update README.md

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Implement credential loading

* Rename credential directory to 'creds'
* Move site info from creds/site/__init__.py to creds/site/__siteinfo__.py
* Add basic saving (not yet implemented)
Merge branch 'master' of https://github.com/lethosor/py-wikibot
Improve command-line logins
Add run_script.py
Add more parameters to Job.format
Implement command_line.new_user

* Add a few API exception classes
* Raise a more useful error when no JSON object is returned from a JSON request
Fix name conflict (command_line.get_user)
Update get_user