Added JsonEncodeOptimizer and JsonDecodeOptimizer. Use PHP internal php_json_encode/php_json_decode implements not userland function call.

Signed-off-by: Rack Lin <racklin@gmail.com>
Merge pull request #78 from racklin/enhancement/json

Added JsonEncodeOptimizer and JsonDecodeOptimizer. Use PHP internal php_...
Merge remote-tracking branch 'upstream/master' into enhancement/strings

Signed-off-by: Rack Lin <racklin@gmail.com>

Conflicts:
	ext/config.m4
	unit-tests/run_tests