Improve performance in json stream parsing

:Release Notes:
Add yajl_dont_validate_strings for Yajl 2.
Custom simple memory pool.
Throughput measurement in MBps.
Add pool of dom parsers.

:Detailed Notes:
Add yajl_dont_validate_strings for Yajl 2.
Memory pool gives us a big win in performance.
Fix performance tests to measure the throughput in MB/s.
Some small improvements and code refactoring.

:Testing Performed:
gtest

:QA Notes:

:Issues Addressed:
[BHV-123] pbnjson: Improve performance of json parsing with YAJL

Open-webOS-DCO-1.0-Signed-off-by: Andrii Zora <andrii.zora@lge.com>

Change-Id: Ic2b49103cf438c77e48f961258e9842fd84fb7d0
Reviewed-on: https://g2g.palm.com/4631
Reviewed-by: DCO Verification
Reviewed-by: Andrii Zora <andrii.zora@lge.com>
Tested-by: Andrii Zora <andrii.zora@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Tested-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>