Feature request: Add crosshair after LivePlotWidget constructor called

[veractor]

When using QtDesigner to design a GUI, the construction of the widgets is done in the generated UI class (if pyuic was used), which means that we don't have a chance to specify any constructor arguments if we don't touch that file.

So after looking through the source code a bit, I've found the only way to add a crosshair to a LivePlotWidget after construction is to do something like this:

widget.crosshair_enabled = True
widget._add_crosshair(pg.mkPen(color='red', width=1), {'color': 'green'})

But this clearly violates encapsulation. Shouldn't there be some way to add a crosshair after construction that would not require calling a privated method?

I believe this was the original motivation behind #13 as well.

[domarm-comat]

Thanks for your comment on this matter.

Yes, adding crosshair after LivePlotWidget was constructed was not straightforward.

I've refactor crosshair code a bit. _add_crosshair became add_crosshair. Now you can simply use:
widget.add_crosshair(pg.mkPen(color='red', width=1), {'color': 'green'})

I also added method widget.remove_crosshair() to easilly remove crosshair from the plot.

It should be available to you in version 0.6.8.

[veractor]

Thank you!