Results 7 issues of Rui Guo

![image](https://user-images.githubusercontent.com/1115061/29234660-35f5fd02-7f2b-11e7-905b-35cff9df0a0a.png) 相关工单:https://leanticket.cn/tickets/13577

Hi, thanks for this great lib. For this PR, I think we need to add a basic timeout when retrieving configurations in URLConfigurationSource. Because `openStream` method of `java.net.URL` will open...

We use regular `FileChannel` to save filters to file. Maybe we can consider to use buffered channel to improve performance which means write bytes to a buffer first then flush...

vegeta: https://github.com/tsenart/vegeta

Support grpc interface in addition to RESTFul APIs.

Maybe we can replicate operations from master to slave. If master fail down, slave can take master's place automatically. filter-service provides RESTFul API, maybe fail over can be a trivial...