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>

cmake rules matters, and fix compile warnings now that we're building
those sources with all the regular flags.

Resolves https://github.com/json-c/json-c/issues/654

Tweak json_parse.c slightly to allow it to build against older json-c versions.

This is intended to provide a way, during development, to test out the memory
and performance impacts of a change.