Column header custom render

[GuiPretto]

Hi! I'm currently using this lib and a feature I really miss is the capability of rendering a custom header for the columns.

So far we can render the column body cells, and adding the column header cell to this group would make this lib even better.

I can do the code, since it's a pretty simple thing. And talking about that, I was thinking of naming this prop as "renderHeader",since "render" already exists for rows cells.

[icflorescu]

Hi!

I believe you can actually render a custom header, since the column's title accepts a ReactNode.
True, it doesn't accept a function returning a ReactNode, but I can't think of a use-case for it. What would its parameters be?

If you can think of a possible usage scenario where you'd need a dynamic title, I guess we could simply refactor the title to accept a ReactNode or a function returning ReactNode instead of adding a new method.

[GuiPretto]

Hey, sorry for not seeing it correctly, since there was no example and the prop was named only "title" I completely forgot to see its type (even though it is right above the render one lol).

I'm gonna make a PR changing it to accept a function as well.

[GuiPretto]

Actually, thinking more about it, I don't really see the need to accept a function, only accepting a ReactNode seems enough.