Add file (line/col) info to ref/relref errors

See #5371

source/position.go

@@ -1,33 +0,0 @@
-// Copyright 2018 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package source
-
-import "fmt"
-
-// Position holds a source position.
-type Position struct {
-	Filename     string // filename, if any
-	Offset       int    // byte offset, starting at 0
-	LineNumber   int    // line number, starting at 1
-	ColumnNumber int    // column number, starting at 1 (character count per line)
-}
-
-func (pos Position) String() string {
-	filename := pos.Filename
-	if filename == "" {
-		filename = "<stream>"
-	}
-	return fmt.Sprintf("%s:%d:%d", filename, pos.LineNumber, pos.ColumnNumber)
-
-}