Add log method output

As an example for the frostfs-node:
```
go run ./cmd -funcs reportFlushError,reportError ../node
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

README.md

@@ -1,2 +1,14 @@
 # log-export
 
+Example for the frostfs-node:
+```
+go run ./cmd -funcs reportFlushError,reportError -dir ../frostfs-node
+```
+
+Command line flags:
+
+```
+-funcs - custom functions to export separated by ','
+
+-dir - source code directory
+```

cmd/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"flag"
 	"fmt"
 	"go/ast"
 	"go/parser"
@@ -8,14 +9,25 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"strings"
+	"sync"
+)
+
+var (
+	customLogs          = flag.String("funcs", "", "Custom functions to export delimited by ','.")
+	directory           = flag.String("dir", "", "Source code directory.")
+	methodsToSearchOnce = &sync.Once{}
+	methodsToSearch     = []string{"Debug", "Info", "Warn", "Error"}
 )
 
 func main() {
-	if len(os.Args) != 2 {
+	flag.Parse()
+
+	if len(*directory) == 0 {
 		log.Fatalln("directory must be provided")
 	}
 
-	directories, err := getAllSubdirectories(os.Args[1])
+	directories, err := getAllSubdirectories(*directory)
 	if err != nil {
 		log.Fatalf("failed to list subdirs: %v", err)
 	}
@@ -33,9 +45,10 @@ func main() {
 					if !ok {
 						return true
 					}
-					if isLogDot(expr.Fun) && len(expr.Args) > 0 && isStringValue(expr.Args[0]) {
+					isLog, logMethod := isLogDot(expr.Fun)
+					if isLog && len(expr.Args) > 0 && isStringValue(expr.Args[0]) {
 						position := fset.Position(expr.Pos())
-						fmt.Printf("%v %s\n", position, stringValue(expr.Args[0]))
+						fmt.Printf("%v %s:%s\n", position, logMethod, stringValue(expr.Args[0]))
 						return false
 					}
 					return true
@@ -73,12 +86,26 @@ func getAllSubdirectories(dir string) ([]string, error) {
 	return result, nil
 }
 
-func isLogDot(expr ast.Expr) bool {
+func isLogDot(expr ast.Expr) (bool, string) {
 	sel, ok := expr.(*ast.SelectorExpr)
-	return ok && (isIdent(sel.Sel, "Debug") ||
-		isIdent(sel.Sel, "Info") ||
-		isIdent(sel.Sel, "Warn") ||
-		isIdent(sel.Sel, "Error"))
+	if !ok {
+		return false, ""
+	}
+	methodsToSearchOnce.Do(func() {
+		for _, cl := range strings.Split(*customLogs, ",") {
+			cl = strings.Trim(cl, " ")
+			if len(cl) > 0 {
+				methodsToSearch = append(methodsToSearch, cl)
+			}
+		}
+	})
+
+	for _, method := range methodsToSearch {
+		if isIdent(sel.Sel, method) {
+			return true, method
+		}
+	}
+	return false, ""
 }
 
 func isIdent(expr ast.Expr, ident string) bool {