add JSON_C_TO_STRING_COLOR option

add JSON_C_TO_STRING_COLOR option

This option enable color in json_object_to_json_string_ext.
I've try to made something similar to jq output,
but I've color true/false and null in purple,
as it's what is common color scheme used in programing language in emacs.

also add a '-c' option into json_parser to test it.

note: that I could have done a color() function similar to
what is done with indent(), but as the code is pretty small
I've keep it as it. so if you want  me to use a subfunction
tell me and I'll do it.

Signed-off-by: Matthias Gatto <matthias.gatto@protonmail.com>