TODO

- Make the OutputFilePath *provider* transactional such that the LFDS can just
  write out whatever it wants and we commit by, say, renaming directories and
  have it implement transaction.ITransactionManager

- Finish the transformer super-classes
- Make `subproperty_of` in class dict work to create rdfs_subpropertyof assignments.
- Define un-zip transformer
- Define an un-tar transformer (may be an un-tar.gz and obviate the next one)
- Define an un-gzip transformer

- Define __format__ for DataSource and DataTranslator to allow for multi-line
vs single line format. 

- Add acc test for source list from a project with a core bundle dep.

- Make agg_store formula-aware

# Bundle commands
- add version number param to OWMBundle::checkout 
- add version number param to OWMBundle::deploy

# Bundle query
- Limit contexts returned from repeated stores with 'excludes' to only list
  excluded (as appropriate. see below)
- Test multiple dependencies excluding/including supersets subsets of each
  others' contexts

- Translate the below into Github issues

- Describe in the documentation the repository, which verifies imported contexts
by downloading them or hashing them

- Describe in the documentation potential "value-added" features that a repo
may implement

- Write an `owm source save` command as a special case of `owm data save` which 

- Make `owm source save` allow to save a directory tree with a user-selected
"data source directory saver" (e.g., an OWMDataSourceDirectorySaver that saves

- Consider distribution schemes that package Python code together with the data

- Add a further specialization for saving data sources that either prompts for,
or accepts on the command line, the fields for the data source

- Write documentation describing the notion of the (current) data context and
(current) imports context

- Contextualize other QueryContext instances with the creating context's context
- Test named data sources in .datasource.transform
- Test project context imports empty bundle context
- Test empty project context imports bundle context