JSON Export

            Rev 1 as of 4.3.15: Initial version
Rev 2 as of 4.3.15: added arrays of strings that are defined by e.g.
list('str1', 'str2')
Rev 3 as of 17.3.15: added support for vectors

    Example usage:

    clear a;
    a.Field1 = 2;
    a.Field2 = "jkh";
    a.Field3 = 1.2;
    a.F3.name = "Joe";
    a.F3.age = 32;
    //a.F3.data = [1,2];
    a.vector = [1,2,3,4.5];
    jsonstr = struct2json(a);
    disp(jsonstr);

    Warning: For strings make sure you escape the special characters that are
used by the JSON-format!

The precision of float values can be adjusted by the command
"format".

Tip: To correctly export NaN values (on Mac or Linux) you could e.g. post
process the json-data (stored in a file) using the sed-command by:

unix('sed -i ''s/%nan/NaN/g'' DataExport.json');