Handling POST requests

1. defined that we expect the encoding of the received data to be UTF-8
2. added an event listener for the “data” event which step by step
fills our new postData variable whenever a new chunk of POST data
arrives
3. moved the call to our router into the end event callback to make
sure it’s only called when all POST data is gathered
4. pass the POST data into the router, because we are going to need it
in our request handlers