Add ReactMarkdownHeading props to resolve #25.
- onChangeHeading -
(headingList: HeadingType[]) => void, Change event handler (optional) - activeHeading -
HeadingType[], Designate active heading list (optional) - activeLiClassName -
string, Class name of the active li tag (optional) - activeAnchorClassName -
string, Class name of the active anchor tag (optional)