[Feature] Step back and forth by one frame

[TomNicholas]

Currently animatplot's animation.controls() supply a play/pause button. It works really nicely, but once the animation is paused you have no option but to resume playing it at the same speed.

What would be great is to add two more buttons, to step one frame forwards or one frame backwards.

Obviously animatplot is not a full GUI, but I think this small change would be within scope and could be unobtrusive. If you used pictorial represenations of the actions then you could probably squeeze the three new buttons required into the same amount of space that the current button occupies. I'm imagining something like ⏪ ▶️ ⏩ (apologies for using emojis to demonstrate).

This shouldn't be hard to do because the buttons just call the _update method.

[t-makaro]

If we add a step forward/back by one, and maybe we should put the buttons in a line below the slider in a row. This would deal with the text of the slider overlapping.

[dcherian]

+5 to buttons below slider. I think it's the most elegant solution

[TomNicholas]

Also it should be possible to use the dragging argument of the slider widget to move a paused animation to a particular frame by dragging it with the mouse...