Allow validator to be called from reads_json and writes_json
Remove if __name__ == '__main__' code from validator
Clean up validator, and rename nbvalidate to validate
Add comments inside validator
Remove unused convert function from validator
Use /notebook as root key
Update nbformat v3 json schema so example notebooks pass
Add isvalid function which returns True/False
Use logging rather than print statements
Update MANIFEST to include schema json file
Use logger string formatting, add some docstrings
Misc style changes, add more docstrings
Remove unused os import
mark v3.withref.json as part of package
Merge pull request #2 from Carreau/nbvalidate

nbvalidate add v3.withref.json to package.
Make sure to pass correct datatype to validate
Distinguish errors during read/write
Remove shebang line because module is no longer callable
Use dirname rather than split
Return the list of errors, rather than the number of errors