add a half violin function

[shangguandong1996]

Dear Developer

I am wondering whether you can add a function which can support plot half vilion like Seurat. I believe it can be useful when you show some gene expression in same cluster in two condition.

Best wishes

Guandong Shang

[alanocallaghan]

I would favour this type of plot over half violins https://github.com/alanocallaghan/scater/issues/175

[shangguandong1996]

Thanks, this type is what I want :)

[shangguandong1996]

Hi, dear developer It seems that the fill_by parametes is in the plotColData. I am wondering plotExpression whether have this parameter.