Helper function for simplifying mapStateToProps

[baron816]

I've written this simple function that I believe simplifies creating mapStateToProps:

export function makeProps(selectors) {
  return function (state, ownProps) {
    return Object.keys(selectors).reduce(function(acc, key) {
      acc[key] = selectors[key](state, ownProps);
      return acc;
    }, {});
  };
}

This will allows me to do const mapStateToProps = makeProps({products, total}); where products and total are selector functions. I believe it's somewhat similar to combineReducers (at least in spirit).

1. There aren't any performance issues that I'm overlooking, are there?
2. Can I add this to react-redux?

[timdorr]

There's already an open PR for this: #724