Problem

I would like to add subtitle and caption to my axis. Currently, afaik the recommended approach is for subtitle to:

1. Use suptitle of figure together with title of the axis.
2. Manually position your own text to define the subtitle.

However, often I have multiple axes for one figure, where I would like to add subtitle to all of them. In this situation, suptitle is not feasible. Also, positioning it using text API can be a bit tedious, especially when having a lot of axes.

With caption, the recommended approach (afaik) is to position it with text. When I do this in practice, I have to manually tune the position for every graph, depending on the value of xlabel.

Proposed solution

It would be great if we had a bit higher-level API for subtitle and caption. They are very comonly needed when plotting the data.

Two new functions on Axis object like set_subtitle and set_caption would be great!