Improve Documentation

[Aklakan]

There are so many features currently either badly documented or just undocumented:

• graphql
• geoindex option
• multiple engine support
• function macros
• in-memory/disk-based caching
• spark-based named graph querying (rpt sansa ngs)
• from enhancer and service enhancer - how to use them
• rmltk how to create output fast (no distinct, no order) and how to have distinct and/or order
• cleanup of releases with broken jars
• documentation of which add-opens flags need to be passed for spark: https://github.com/SmartDataAnalytics/RdfProcessingToolkit/blob/jena-5.0.0/rdf-processing-toolkit-pkg-parent/rdf-processing-toolkit-pkg-deb-cli/src/deb/resources/usr/bin/rpt#L12

There should be dedicated sections for how to use rpt in different architecture setups; e.g. as a caching proxy.

Thanks to @SimonBin the maven build produces ascii documentation files for the picocli commands, but they need to be added to the ...

• documentation web page.
• deb / rpm packaging