Speciy p and q when executing embed instead of during creation

[RemyLau]

Originally done so following the node2vec source code. It makes sense to specify these parameters during the embedding function call, so that when embedding with different settings of p and q, we do not need to load the save graph object over and over again.

The only catch is that for PreComp, need to make sure each time we change the p and q settings, we need to rerun the preprocessing function.

[RemyLau]

Leave workers, verbose, extend as optional input to __init__, those could be fixed at creation time