Setting the names of x axis and y axis

[pedroallenrevez]

Right now in order to change the name of the axis you have lots of ways to do it:

• Sending in a tuple (col, col_name) to any hv.Callback
• redim.label
• finalize hooks
• and possibly many others that I'm not aware of

I think it would greatly simplify things for the user if one could pass x_label and y_label to the callback.

Thanks.

[philippjfr]

xlabel and ylabel are now supported as plot options.