Add GraphFrame.node2vec() method from Mercury Graph

[Russell Jurney]

Hello my peeps,

I wanted to bring your attention to a new feature I outlined in Issue #484. I want to borrow the code for Mercury Graph's Apache 2 licensed Node2Vec method that is a fairly simple implementation on top of Spark MLlib's Word2Vec feature.

I wanted to raise this for discussion. What do we think about borrowing Apache 2 licensed code, with attribution? In practice I would rewrite the code, it is mainly a guide to implementing the feature. Alternatively we would create a graphframes.mercury module and integrate their features there... thoughts?

See: Issue #484 - Add Node2Vec from Mercury Graph as GraphFrame.node2vec() method

Thanks,

Russell