Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

reader/atom/parser.go

@@ -1,61 +0,0 @@
-// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
-// SPDX-License-Identifier: Apache-2.0
-
-package atom // import "miniflux.app/v2/reader/atom"
-
-import (
-	"bytes"
-	"encoding/xml"
-	"io"
-
-	"miniflux.app/v2/errors"
-	"miniflux.app/v2/model"
-	xml_decoder "miniflux.app/v2/reader/xml"
-)
-
-type atomFeed interface {
-	Transform(baseURL string) *model.Feed
-}
-
-// Parse returns a normalized feed struct from a Atom feed.
-func Parse(baseURL string, r io.Reader) (*model.Feed, *errors.LocalizedError) {
-	var buf bytes.Buffer
-	tee := io.TeeReader(r, &buf)
-
-	var rawFeed atomFeed
-	if getAtomFeedVersion(tee) == "0.3" {
-		rawFeed = new(atom03Feed)
-	} else {
-		rawFeed = new(atom10Feed)
-	}
-
-	decoder := xml_decoder.NewDecoder(&buf)
-	err := decoder.Decode(rawFeed)
-	if err != nil {
-		return nil, errors.NewLocalizedError("Unable to parse Atom feed: %q", err)
-	}
-
-	return rawFeed.Transform(baseURL), nil
-}
-
-func getAtomFeedVersion(data io.Reader) string {
-	decoder := xml_decoder.NewDecoder(data)
-	for {
-		token, _ := decoder.Token()
-		if token == nil {
-			break
-		}
-
-		if element, ok := token.(xml.StartElement); ok {
-			if element.Name.Local == "feed" {
-				for _, attr := range element.Attr {
-					if attr.Name.Local == "version" && attr.Value == "0.3" {
-						return "0.3"
-					}
-				}
-				return "1.0"
-			}
-		}
-	}
-	return "1.0"
-}