add numeric comparison for 'if' directive
bumped to 2.0.0 version
Merge pull request #316 from yaoweibin/bump-tengine-2.0

bumped to 2.0.0 version
add test cases for numeric comparison of 'if' directive
add some abnormal test cases
Merge pull request #315 from flygoast/master

add numeric comparison for 'if' directive
use configurable persistent connection in upstream health check
Merge pull request #321 from lilbedwin/health_check

use configurable persistent connection in upstream health check