Support for soft clustering

[Moonire]

add's the option to keep overlapping nodes in the clustering or to delete their duplicates by setting keep_overlap either to True or False. Displaying a message informing the user that there are overlaps in case he is using the default hard clustering method.

[GuyAllard]

Hi Mounir, Thanks for submitting this PR.

I would like to approach this slightly differently to your implementation.

Specifically, I would like to perform the identification and removal of overlap nodes in a separate function which is called when keep_overlap=False Doing so will make the code easier to maintain and test.

What are your thoughts on this approach?

[Moonire]

It seems perfectly reasonable to me. In this case I think a ternary operator that will call the function when keep_overlap=False will do the trick. I'll take care of that asap.

Do you want to change the warning message ? I know i'm not good with writing warnings haha.

[codykingham]

It seems a fix for this was never implemented?