include cmath only under C++11 (#36)
include cmath only under C++11 (#36)

Banchi0123/picojson,karya0/picojson,kazuho/picojson,karya0/picojson,pfultz2/picojson,Banchi0123/picojson,turenar/picojson,turenar/picojson,kazuho/picojson,pfultz2/picojson