codec: json: encode Nan, +Inf or -Inf as null
codec: json: encode Nan, +Inf or -Inf as null

This is in line with NOTE 4 of the ECMA-262 ECMAScript Language Specification 5.1 edition.
see http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf .

ugorji/go,ugorji/go,ugorji/go