Add option for action type transforming

[arusakov]

Hi, thank a lot for great logger!

Option for action type transforming will be helpful, if action type is a number (for example, member of some enum). In this case for pretty logging you can provide typeToString function like this:

const enum = {
  1: 'action_one',
  2: 'action_two',
  action_one: 1,
  action_two: 2
};

import createLogger from 'redux-logger';
const logger = createLogger({
  typeToString: (type) => enum[type]
});

// ...
// and somewhere in app
dispatch({type: enum.action_one});

[imevro]

Hi, thanks for idea. Will release in 1.1.0 tomorrow!