This was a decision on my part ... and this badly needs documentation 

Here's what i implemented: 
Line 51: the delete character u007f is changed to a really ugly xfffd character
Line 57: control characters 0x00 - 0x20 will be changed to a really ugly xfffd character

when we unencode, we don't know what to unencode to. 
IMO, it's better to unencode to the less ugly 007f character.

xfffd is used 
http://www.fileformat.info/info/unicode/char/fffd/index.htm