Folia

Another round of significant fixes and refactoring in the wake of the v2 release, mostly to do with backward compatibility. One notable change: this release changes the default value for ``set`` in a lot of functions. Set is now ``False`` when it means *any set* (useful in querying functions), it is ``None`` to specifically mean *no set/setless* and of course a string with ideally (but not necessarily) a URL in all other cases.

Various more fixes and refactoring in the wake of the FoLiA v2 release:
* Fixed autodeclaration of setless elements

Small fix for backward compatibility in serialisation of FoLiA v1

Updated documentation and minor fixes for FoLiA 2.0.1

Allow (limited!) serialisation of older FoLiA versions if ``keepversion`` is set.

Major new release; the former ``pynlpl.formats.folia`` module in PyNLPl has now been migrated to this new standalone package, which constitutes the new FoLiA library for Python. Included is the FoLiA library, FQL library and Set Definition library. This release implements the new FoLiA v2.0, consult the release notes there for a comprehensive list of changes. Library documentation is now hosted on https://foliapy.readthedocs.io/en/latest/.
Upgrading from pynlpl is usually as easy as doing a ``pip install folia`` and replace within your software: ``from pynlpl.formats import folia`` with ``import folia.main as folia``. The library is backward compatible.