fix tests
add prototype of hook system
improve error handling
add hook point: pre_http_push
use metadata as http response header
add hook module for preserving http headers
add new property: hooks
unregister hooks that not included in new config
run hooks in another process
Merge pull request #36 from nora/feature/hook-system

Introduce hook system
Fix updating parameters of a hook, closes #37
Add initial version of InfluxDB support
Merge pull request #39 from nora/feature/influxdb-support

Add initial version of InfluxDB support
Fix stats to contain the queue name
Pin the cowboy version