[#12] Make sure vocabs can be updated from JSON files.

Allow JSON file path to be specified on command
line.

Some other small code clean up.
[#12] Remove 'import-publishers' command as 'update-publishers'
performs the same task.
[#12] Remove 'import-data' command as no longer used.
[#12] Allow path to publisher file to be specified for 'update-publishers' command.

Do not call 'update-publishers' during 'create-all-vocabs' command.
[#12] Remove 'export-datasets' command as is now in CKAN core
[#12] Change 'create-*' vocab commands to 'update-*'.
[#12] Update README
[#12] Delete vocab tags that are removed from the vocab JSON files