Add options to control size of names of columns and rows of the heatmap

[LucasMS]

With longer names on the columns and rows in the heatmap, I observed that the names were badly positioned, hidden behind the heatmap. Could not find a way to adjust this.

Thanks for the good work :)

[rlbarter]

This should be possible using the left.label.text.size and .bottom.label.text.size arguments. See the vignette section on this: https://rlbarter.github.io/superheat/labels.html#label-text-size.

[LucasMS]

Thanks :)