Pull request: all: less annoying pkg names

Merge in DNS/adguard-home from imp-naming to master

Squashed commit of the following:

commit d9e75c37af9a738384393735c141a41406d22eeb
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu May 13 15:52:14 2021 +0300

    all: less annoying pkg names

internal/filtering/README.md

@@ -0,0 +1,70 @@
+# AdGuard Home's DNS filtering go library
+
+Example use:
+```bash
+[ -z "$GOPATH" ] && export GOPATH=$HOME/go
+go get -d github.com/AdguardTeam/AdGuardHome/filtering
+```
+
+Create file filter.go
+```filter.go
+package main
+
+import (
+    "github.com/AdguardTeam/AdGuardHome/filtering"
+    "log"
+)
+
+func main() {
+    filter := filtering.New()
+    filter.AddRule("||dou*ck.net^")
+    host := "www.doubleclick.net"
+    res, err := filter.CheckHost(host)
+    if err != nil {
+        // temporary failure
+        log.Fatalf("Failed to check host %q: %s", host, err)
+    }
+    if res.IsFiltered {
+        log.Printf("Host %s is filtered, reason - %q, matched rule: %q", host, res.Reason, res.Rule)
+    } else {
+        log.Printf("Host %s is not filtered, reason - %q", host, res.Reason)
+    }
+}
+```
+
+And then run it:
+```bash
+go run filter.go
+```
+
+You will get:
+```
+2000/01/01 00:00:00 Host www.doubleclick.net is filtered, reason - 'FilteredBlackList', matched rule: '||dou*ck.net^'
+```
+
+You can also enable checking against AdGuard's SafeBrowsing:
+
+```go
+package main
+
+import (
+    "github.com/AdguardTeam/AdGuardHome/filtering"
+    "log"
+)
+
+func main() {
+    filter := filtering.New()
+    filter.EnableSafeBrowsing()
+    host := "wmconvirus.narod.ru" // hostname for testing safebrowsing
+    res, err := filter.CheckHost(host)
+    if err != nil {
+        // temporary failure
+        log.Fatalf("Failed to check host %q: %s", host, err)
+    }
+    if res.IsFiltered {
+        log.Printf("Host %s is filtered, reason - %q, matched rule: %q", host, res.Reason, res.Rule)
+    } else {
+        log.Printf("Host %s is not filtered, reason - %q", host, res.Reason)
+    }
+}
+```