Add backend weight round robin select (#34)

* Add upstream selector, there are two selector now:
    - random selector
    - weight random selector

random selector will choose upstream at random; weight random selector will choose upstream at random with weight

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Rewrite config and config file example, prepare for weight round robbin selector

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Replace bad implement of weight random selector with weight round robbin selector, the algorithm is nginx weight round robbin like

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Use new config module

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Disable deprecated DualStack set

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Fix typo

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Optimize upstreamSelector judge

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Fix typo

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Add config timeout unit tips

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Set wrr http client timeout to replace http request timeout

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Add weight value range

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Add a line ending for .gitignore

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Optimize config file style

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Modify Weight type to int32

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Add upstreamError

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Rewrite Selector interface and wrr implement

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Use http module predefined constant to judge req.response.StatusCode

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Use Selector.ReportUpstreamError to report upstream error for evaluation loop in real time

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Make client selector field private

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Replace config file url to URL
Add miss space for 'weight= 50'

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Rewrite Selector.ReportUpstreamError to Selector.ReportUpstreamStatus, report upstream ok in real time

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Fix checkIETFResponse: if upstream OK, won't increase weight

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

* Fix typo

Signed-off-by: Sherlock Holo <sherlockya@gmail.com>

doh-client/main.go

@@ -32,6 +32,8 @@ import (
 	"os"
 	"runtime"
 	"strconv"
+
+	"github.com/m13253/dns-over-https/doh-client/config"
 )
 
 func checkPIDFile(pidFile string) (bool, error) {
@@ -101,13 +103,13 @@ func main() {
 		}
 	}
 
-	conf, err := loadConfig(*confPath)
+	conf, err := config.LoadConfig(*confPath)
 	if err != nil {
 		log.Fatalln(err)
 	}
 
 	if *verbose {
-		conf.Verbose = true
+		conf.Other.Verbose = true
 	}
 
 	client, err := NewClient(conf)