konigsberg_graph: Create a road and bridge network from OSM data
In dSHARP-CMU/konigsbergr: Find Paths Through Bridges On A Map

Creates a base graph object with the appropriate edge and vertex attributes from OSM.

1 2	konigsberg_graph(src, path_filter = automobile_highways, bridge_filter = all_bridges)

`src`	An `osmar` or a `base_konigsberg_graph` object.
`path_filter`	A function that filters which Ways will be traversable in the graph. See `way_filters`.
`bridge_filter`	A function that marks which Ways are bridges that need to be crossed. See `bridge_filters`.