Function zoomSymlog

docs/app/js/sanddance-app.js:106722–106724

(domain, anchor, scale, constant2)

    return zoom(domain, anchor, scale, pow(exponent), pow(1 / exponent));
}
function zoomSymlog(domain, anchor, scale, constant2) {
    return zoom(domain, anchor, scale, symlog(constant2), symexp(constant2));
}
function quarter(date) {
    return 1 + ~~(new Date(date).getMonth() / 3);
}