Feature: Multigraphs

[LuaiKam]

Hi bitwalker,
Thank you for this amazing hex package, am looking to create multigraph(multi edges between same ends with diff edges data) and as well label edge coloring.

is there any future plans to support it?

[bitwalker]

I considered it when building the library, but haven't had time to revisit it. I'm open to working with someone on getting a PR merged for adding such support though!