undirected graph should support 'connectsFrom'

[moaxcp]

connectsFrom creates an edge with 'two' set to the current vertex. It is the opposite of connectsTo where 'one' is set to the current vertex. It is useful for undirected graph to support this in the case that it is later converted to a directed graph.

vertex('A') {
    connectsFrom('B")
}

creates edge from 'B' to 'A' in an undirected graph.