Add option to disable axes individually

[omarkhan]

I need to hide only the y axis labels. I tried setting yLabelFormat to a function that returns the empty string, but that broke the number displayed in the hover popup.

This patch extends the axes option to allow true, false, 'both', 'x', or 'y'

[tiraeth]

I would go with different values for axes instead of separate options, like:

• true or both for both enabled
• false for both disabled
• x for X enabled, Y disabled
• y for X disabled, Y enabled

The advantage of the proposed solution is that we're not introducing BCB (you don't do so either but this don't add additional options).

[omarkhan]

@tiraeth done in d142048

[oesmith]

Awesome work again! If you could do another PR for docs, that would be amazing 👍

Thanks!