pep8
support for listing article versions
support for adding links

can add multiple links; won't add links that already exist
article() returns the items
default creation is a dataset rather than fileset
make calls to API in a more uniform manner

- save the response object for debugging
- always return response.json()
- strip docs (which will be summarized later at class level)
support for add/remove author, category, tag
support for showing versions and categories
docs
Merge pull request #4 from daler/master

finish adding API features