Invert arc labels

[J7mbo]

Hi! Firstly, thank you for taking over this library. It's super useful (and is teaching me a lot about charts, haven't really used them before this).

There is an open pull request (code here) in the unmaintained version of this lib that flips the labels underneath the arcs where the text would otherwise be upside down. However, this code is no longer compatible with the updates you've made to this lib, so it's not easy for me to migrate over.

Please would you consider porting this to allow the text to be flipped at the bottom of the arc? Or is this functionality already in here somewhere?

[J7mbo]

Actually, the code does just paste over and work as nothing is modified here. Must've been looking at another library. I would try and put in a PR but I'm guessing you would like this as an option not a default; how would you like to do that (If there's any interest in this feature anyway).

[DavideViolante]

The code is not so different from the old repo, I think you can open a PR here and I will check it out. Thanks