Node connected to itself with default lifestyle looks not great.

[NAThompson]

(Firstly this library is awesome, so hopefully this doesn't come across as ungracious.)

If a node is connected to itself in a graph with the default linetype, the graph looks weird. However, if linetype=curve, then the graph looks great yet again.

Proposing to default the linetype to curve for an edge which originates and ends with the same node.

[hdavid16]

@NAThompson thank you for this feedback. This is fixed in PR #186, which will hopefully be reviewed someday and merged.