some usability tweaks

improved dev server behavior, cleaned up readme, fixed twisted deprecation warnings.

Just fixed some little rough edges I found when using hendrix as a devserver.
It was printing:
```
Starting Hendrix...
Starting Hendrix...
Ready and Listening...
```

There was a deprecation warning about modifying received_headers.  I think I implemented the equivalent using the newly suggested method.

```
hendrix/hendrix/contrib/cache/resource.py:284: DeprecationWarning: twisted.web.http.Request.received_headers was deprecated in Twisted 13.2.0: Please use twisted.web.http.Request.requestHeaders instead.
```

And I cleaned up the read me a lot.  I know it's subjective but I found it a little bit scary!
In my opinion, it works better now.  Starts with the TLDR and if you want more info, you can keep scrolling.