Support Blank Nodes

[NoelDeMartin]

Blank nodes are currently not supported, so there is no way to parse or create data such as this with the library (even though it's valid RDF):

@prefix schema: <https://schema.org/>.
@prefix XML: <http://www.w3.org/2001/XMLSchema#>.

<#it>
    a schema:Movie;
    schema:name "Spirited Away".

[
    a schema:WatchAction;
    schema:object <#it>;
    schema:startTime "2020-12-10T19:20:57Z"^^XML:dateTime.
]