[JSON::PP] 2.05

• enhanced some XS compatibilities for de/encode.
  
• now decode_error can dump high (>127) chars.
  
• enhanced the XS combatilbity of the decoding error.
  
• fixed the utf8 checker while decoding (is_valid_utf8).
  
• implemented utf8::downgrade in JSON::PP56.
  
• enhanced utf8::encode in JSON::PP56.
  
• made utf8::downgrade return a true in JSON::PP5005.