json: Export printbuf APIs for future use

The "printbuf" API is useful for bug2issue to generate formatted json object
content. This patch exports such APIs for future usage.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
json: Export array APIs for future use

The array API is useful for bug2issue to store simple "close-status" array.
This patch exports such APIs for future usage.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>