docs do not state at what version an API was introduced (or deprecated)

An all-to-common problem for new developers coming to the TinkerPop is figuring out which APIs work against the graph they are using. Since TinkerPop is ahead of many graph implementation out there (Titan/TP 3.0.1, Stardog/TP 3.0.2, Blazegraph/TP 3.1.0 – kudos to Sqlg and Unipop for TP 3.2.0!), it's really important that developers know which APIs in the current docs are valid. Ideally the developers would go directly to that version of the TP docs, but that doesn't always happen thanks to Google.

I propose doc updates on each Graph Traversal Step in the reference docs and in the javadocs (on __.java and on specific step implementations, i.e. AddEdgeStep.java).

It should state the specific version (3.y.z) the API was introduced or deprecated.