GMNS 0.96, using Frictionless to automatically generate documentation

[ssmith55]

he GMNS specification is defined in a set of json files, one for each table. Release 0.96 uses Frictionless to automatically generate the following usable artifacts:

• Human-readable markdown files (resolves issue Auto-generate md documentation #64)
• An optional empty SQLite database to hold a network formatted in accordance with GMNS. This is an convenience for users who may wish to exchange GMNS-formatted networks via databases rather than .csv files.
• SQL create statements The database and create statements are placed in usage/database https://github.com/zephyr-data-specs/GMNS/tree/develop/usage/database
• Documentation, placed in https://zephyr-data-specs.github.io/GMNS/ (partially addresses issue Add user-readable documentation website #65)

In the json files, the ID fields (node_id, link_id, etc.) has always been defined as type "any", allowing text or integer to be used. This follows the example of unique_ID as defined in GTFS. It is certainly possible that an application may further restrict ID fields to be integer (issue #83).

The automated generation of markdown has resulted in several non-substantive changes to the markdown files:

• Their names are in lower case (e.g., node.md) rather than mixed case (e.g., Node.id)
• Datatypes for the ID fields are "any", carried straight from the json files
• Datatypes are number (rather than numeric), string (rather than text)

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