Feature request: Customize the start of the arrow

[mikaello]

Related to #39. It would be great if it where possible to customize the beginning/start/origin of the arrow. E.g. it could be added a circle at the beginning to mark the attachment of the arrow at some object:

[pierpo]

It would make perfect sense indeed!
PRs are welcome, otherwise I'll have a look when I find the time 😉

Thanks for the suggestion!