Log Message:
Update package to latest version, 2.5. Changes include:
* Use ipaddr
* Support "Expect: 100-continue"
* fix PID file
* fix VERSION
* Support for DELETE and PUT http method
* Support syslog logs
* option for ipv4/v6 in ocsigen_http_client
* Prevent exit when an Lwt.async task raise an exception
* fix HTTP bytes range (#8)