Xxencoding is obsolete but still included for completeness. Further information on the encoding can be found at http://en.wikipedia.org/wiki/Xxencode. It should be noted that this implementation performs no padding, due to the splitting up between encoding and chopping.
Further documentation and information can be found at http://www.haskell.org/haskellwiki/Library/Data_encoding.
Chop up a string in parts. Each string in the resulting list is prepended with the length according to the xxencode "specificiation".