export output data in true json format

[yannrichet]

Fix x1= [.1,2,3] in "x1":[0.1,2,3]

[yannrichet]

funz-core/src/main/java/org/funz/util/Data.java

Line 116 in 01441fc

buf.append(cast[i]);

to avoid ".5", and force "0.5", something like:

DecimalFormat formatter = new DecimalFormat("#0.0#");
double d = 0.50;
System.out.println(formatter.format(d));