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

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

Update hot-spot param flow example

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

Polish circuit breaking and "hot spot" param flow example

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

Sentinel Go 0.3.0

Sentinel Go 0.2.0

Sentinel Golang 0.1.0