implementing email notifications

Implementing e-mail notifications.
Use it like:
```javascript
var logger = require('./index').createLogger({
  console: {
    color: true
  },
  email: {
    smtp: '<smtp server>',
    address: '<your email address>',
    username: '<username>',
    password: '<password>'
  }
});

logger.error('503: Error message!').email();
```

It sends an e-mail from the given address to the given address. The E-Mail looks like:
````