doc: add utils 'er' and 'wrStringAndCheck'

doc/util.go

@@ -14,6 +14,7 @@
 package doc
 
 import (
+	"io"
 	"strings"
 
 	"github.com/spf13/cobra"
@@ -49,3 +50,11 @@ type byName []*cobra.Command
 func (s byName) Len() int           { return len(s) }
 func (s byName) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
 func (s byName) Less(i, j int) bool { return s[i].Name() < s[j].Name() }
+
+func er(msg interface{}) {
+	cobra.Er(msg)
+}
+
+func wrStringAndCheck(b io.StringWriter, s string) {
+	cobra.WrStringAndCheck(b, s)
+}