Bugs and enhancements

[GreatYYX]

Bugs:

• RDF prefix does not work properly: some URIs get converted to prefix:fragment, some are ns1:fragment (this is ok according to the definition of W3C), but some are still the full URIs.
• Some BNodes still show arbitrary IDs (would be better if BNode is shown as "blank").

Enhancements:

• Support converting a node to BNode based on regex. e.g., there are <URI1> <URI2> <URI3>, but I don't want to see the full URI of URI1, then I can add this filter and it will be converted to a BNode which will show as "blank". Notice this is not blacklist, because I still want to see this node but just don't want to see it's full URI.
• Blacklist supports only subjects and objects (I'm not sure here), it would be better to support all subject, predicate and object URIs. Also, if a node has no connection (e.g., all its predicates are in blacklist), it can be hidden (I think this should be an option).

BTW, correct me if the feature is already there or I used it in the wrong way.

[GreatYYX]

Forgot to mention, would be better to add some useful commands of graphviz, like how to organize nodes in graph, to readme file.