can't style sendmessageleftx

[tobiasBora]

First, thanks for this package.

The sendmessage allows me to define my own style for the arrow to replace sendmessageleft, which is great (for instance to change the arrow style, like having tips on both ends, or the spacing). However, as far as I can see, the multicolumn version sendmessageleftx can't be styled, (and I don't think that sendmessage can be used on multiple columns). Would it be possible to provide an interface like sendmessage for multicolumns?