Folia-tools

* foliaupgrade: refactoring and updates
* foliaupgrade: set src and format attributes on pre-upgraded version
* foliavalidator: add proof of validation (not cryptographical) to provenance chain (only when --output is chosen)
* folia2html: updated for FoLiA v2

* foliacat: More provenance data for foliacat
* foliacat: Compatibility for serialising older FoLiA versions
* Added conllu2folia tool (1)
* implemented foliaupgrade, convert old-style annotator data to provenance

Minor refactoring of foliacat and better version reporting

* Fix for foliacat when dealing with older versions

Enable keepversion for certain tools, so they don't upgrade to FoliA v2 if FoLiA v1 input is given, ensuring better backward compatibility.

This is the FoLiA v2 version of the FoLiA-tools, now split from the central FoLiA repository at https://github.com/proycon/folia and building on the new FoLiApy library. New documented resides at https://folia-tools.readthedocs.io/

* There is a new ``foliaupgrade`` tool to upgrade from FoLiA v1 (or v0) to v2 (although this is usually done implicitly by any of the other tools, or the FoLiAPy library itself, anyway)
* Refactored the entire foliavalidator
* Cleaner output without stack traces from FoLiA validator (proycon/folia44)
* Added automatic injection of provenance information to various tools