Ban system metric collector for windows OS(alibaba#312)

Make map&slice with init capacity to decrease grow cost (alibaba#273)

* refine code

Co-authored-by: louyuting <[email protected]>

Support arbitrary statistic duration for flow control and refactor in…

…ternal implementation (alibaba#200)

* Support arbitrary statistic duration for flow control. Add `StatIntervalInMs` attribute in flow.Rule. When StatIntervalInMs > globalInterval or < bucketLength, we create a new sliding window for it.
* Add stat reuse mechanism for flow rules
* Make threshold of flow rule "request amount per interval" rather than QPS.
* Refine internal implementation

Add doc.go for core/api, flow and circuitbreaker package (alibaba#235)

Add package-level document for api and adapter/micro package

Signed-off-by: Eric Zhao <[email protected]>

Update hot-spot param flow example

Signed-off-by: Eric Zhao <[email protected]>

Polish circuit breaking and "hot spot" param flow example

Signed-off-by: Eric Zhao <[email protected]>

Sentinel Go 0.3.0

Sentinel Go 0.2.0

Sentinel Golang 0.1.0