API Enhancements

Updated the API to behave more like express using switched.

var bus = require('bus.io');
bus.on('some*', function (msg, next) {
  next();
});
bus.on(/event/, function (msg, next) {
  next(new Error('Some Error'));
});
bus.on(function (err, msg, next) {
  next();
});
bus.on('some event', function (msg, next) {
  msg.deliver();
});