Refactor

Move json_value and obj_t to same file
 - Rename json_obj.* -> json_value.*
 - Move `print_json_value(...)` to json_value.*

Move `err_ctx(...)` to util.*

parse.h now only exposes `parse_json_value(...)`

src/main.c

@@ -1,5 +1,5 @@
 
-#include "json_obj.h"
+#include "json_value.h"
 #include "parse.h"
 #include "util.h"