support single edge/node label

[khoale88]

• support single edge label matching. This requires the host graph to have __labels__ set as a set. Otherwise, errors can be raised or no matches can be found
• support single node label matching. This requires the host graph to have __labels__ set as a set. Otherwise, errors can be raised or no matches can be found
• return an explicit edge-hop relation is always a list of relations regardless the hop step.
• promote node json condition to is_node_attr_match
• support for True/False values

[khoale88]

hi @j6k4m8 , I think the PR is good enough. Can you take a look? You can compare the result against neo4j to see if I miss anything important.
https://console.neo4j.org/

[j6k4m8]

This is great, sorry for the delay! (I have been traveling)