Somewhat significant rewrite and PEP8 fixes

* Use unix line endings
* Remove unused variables
* Adhere to PEP8 (mostly around line length)
* Simplified a LOT of XML generation
* Added an RX473.off method, to turn off the unit
* Added an RX473.volume_fade method, to gradually fade the volume
  to the specified dB level
* Removed hardcoded IP address in class
* Revised main with simpler and tested example