Accept OME-XML types without OMERO

[multimeric]

I'm hoping to leverage some of the work in this repo to take OME-XML metadata and convert it into RDF.

e.g. I'd ideally be after something like this:

from ome_types import OME
from rdflib import Graph

def ome_to_rdf(OME) -> Graph: pass

Which I would use like this:

from ome_types import from_tiff
from omero_rdf import ome_to_rdf

ome = from_tiff("image.tiff")
ome_to_rdf().serialize(...)

Happy to help implement this if you think it fits in here.