[JSON::PP]

• decode() didn't upgrade unicode escaped charcters \u0080-\u00ff.
  this problem was pointed by rt#43424 (Mika Raento)
  [JSON::PP::56]
  
• fixed utf8::encode/decode emulators bugs.
  
• defined a missing B module constant in Perl 5.6.0.
  (reported by Clinton Pierce)
  [JSON::PP::5005]
  
• _decode_unicode() returned a 0x80-0xff value as UTF8 encoded byte.
  [JSON]
  
• added a refference to JSON::XS's document "JSON and ECMAscript".
  
• fixed a typo in the document (pointed by Jim Cromie).