Adding Inneighbour and Outneighbour functions for OSMGraph

[ThatDezKnightGuy]

The lightOSM OSMGraph is an abstraction of the underlying graph, but it is missing a few of the normal methods of interacting with graph traversal.

A good enhancement would be implementing the inneighbours and outneighbours functions from LightGraphs interfaces to remove dependencies on these functions elsewhere. The functiuons can be wrappers of the functions to pull out the in and out neighbours of the OSMGraph.graph, and it would be good if there were dispatches to let you choose between the OSM node id and the vertex index of the graph.