I was just about to create a PR with the support for this same feature =)
We could've made it fully compatible with Echarts by adding bool variants:

pub enum Step {
    True,
    False,
    Start,
    Middle,
    End,
}

impl From<bool> for Step {
    fn from(value: bool) -> Self {
        if value {
            Step::True
        } else {
            Step::False
        }
    }
}

Ah, although maybe I'm missing the serialization part, true and false would have to become boolean literals rather than strings, anyway, just a suggestion

This would be correct. It should be fairly easy and examples of it are in the repo.

I will take a look at this PR and merge it at the start of next week.

@cooljingle Do you want to implement the suggestion from grinya, the implementation From<bool> and the correct serialization of Step::True and Step::False?