Add optional marker icons and labels

[kfox]

Description

Sometimes it would be helpful to represent more information about the effects of changing a slider's value by using labels or icons (or both) centered above or below specific slider values. For instance, certain values along a slider axis might represent various "presets", e.g. "small", "medium", or "large" sizes, various "standard" levels of image opacity, etc., but you may also want to preserve the ability to select things in-between those preset values.

Live Demo and Documentation

Demo of my paper-slider feature branch

Examples