fix #1, remove "--jsondatafile=" from CLI syntax

Usage: jsoncppgenerator.py [options] JSONFile

Options:
  -h, --help       show this help message and exit
  --dstdir=DSTDIR  directory to save the generated code files, default is
                   current directory
  --gentest        generate test code "main.cpp", default is false
for python 3 support (#8), fix type()
fix #9, remove unused Print() from generated code
fix #10, add isPrettyPrint to generated EncodeJSON