rdf to-jelly: implement jelly-text as an input format

[Ostrzyciel]

Extension: .jelly.txt or .jelly-txt

This would be useful in producing invalid Jelly files for testing purposes, for example. Or for fine tuning certain options.

Of course, the text format is not stable. I'd suggest emitting a warning on stderr every time we use this parser, that it's unstable and should not be used in production.

WARNING: The Jelly text format is not stable and may change in incompatible ways in the future. It's only intended for testing and development. NEVER use it in production.

Don't worry, it's stderr, so it won't end up in the Jelly file.

There should be a --quiet common option to silence this and other warnings.

[Ostrzyciel]

@Karolina-Bogacka are planning to implement this as part of #45 ?

What's the status on that?

I'm just wondering if I should do this first or not.

[Karolina-Bogacka]

No, I haven't included it in #45 - as written in the issue I have limited myself to Jena-compatible formats