Introduce semantic versioning on generated rdf

[andrawaag]

In #38 an issue with the chosen schema emerged. The fix needed a substantial change that it will probably introduce breaking changes in querying.

I propose to introduce semantic versioning. Since it is intended primarily for software development I propose to following definition when applied on data:

Given a version number MAJOR.MINOR.PATCH, increment the:

MAJOR version when you make a completely new schema.
MINOR version when you reshuffle a single branch
PATCH version when you make a change on a single node or triple.

Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format.

[joshmoore]

Looking at the implementation, there's the version of the XLSX file itself, but also of the generation code, right?

[andrawaag]

Building @joshmoore point I adapted the schema to capture provenance of the source file (xls), the resulting RDF triples and the python script that generates the triples from the provided xls data.