src/lib.js
function getAllSelectors(css) {
    let selectors = [];
    css.walkRules((rule) => {
        selectors = _.concat(selectors, rule.selector);
    });
    return selectors;
}
function getAllSelectors(css) {
    let selectors = [];
    css.walkRules((rule) => {
        selectors = _.concat(selectors, rule.selector);
    });
    return selectors;
}
Get all the selectors mentioned in {css}
@param  {Object} css        The postcss.Root node
@return {Array}