Update Gherkinize to create a summary of tests with and without WIP status

[slott56]

Since the documentation uses RST, which has a .. csv-table:: directive, the Gherkinize CLI should include a --summary <filename> option, which will write the summary table.

Tentatively, the table should follow the feature/scenario hierarchy with a ✅ with no WIP, and ❌ to show a test excluded because it flagged @WIP.

[slott56]

Gherkinize is used on a number of individual feature files, controlled by make. This means that each run of Gherkinize will produce a revised .feature file and a .csv summary of the features included in the feature file.

The final documentation production can then aggregate the .csv files. Either cat them into a single file, or use multiple .. csv-table:: directives to include all of them into the final documentation.

[slott56]

Closed by #191