styled-components/src/vendor/postcss/warn-once.js

**This is a work in progress** based off of [this demo](https://github.com/geelen/css-components-demo).

let printed = { };

export default function warnOnce(message) {
    if ( printed[message] ) return;
    printed[message] = true;

    if ( typeof console !== 'undefined' && console.warn ) console.warn(message);
}