4.8.1

1. Support new JSON format, produced with newest TBufferJSON
   • object references stored as {"$ref":12}
   • pair objects for std::map marked with "$pair" : "pair<type1,type2>" data member
   • old JSON format will be recognized automatically and supported as well
2. Fix - better selection of Y range for log scale
3. Provide JSROOT.parse_multi() function to correctly parse response of multi.json request,
   support it in the JSROOT.NewHttpRequest method as well.
4. Fix - correctly calculate integral for TH1
5. Partially support new TFormula with complex C code inside