Move song header into separate file

internal/song/header.go

@@ -0,0 +1,37 @@
+package song
+
+import (
+	"github.com/yuin/goldmark/ast"
+)
+
+type Header struct {
+	tableHeader *ast.Node
+}
+
+func NewHeader(h *ast.Node) Header {
+	return Header{tableHeader: h}
+}
+
+func (h Header) Remove() Header {
+	h.tableHeader = nil
+	return h
+}
+
+func (h Header) RemoveColumns(idx Indexes) Header {
+	if !h.Empty() {
+		removed := RemoveCols(idx, *h.tableHeader)
+		h.tableHeader = &removed
+	}
+	return h
+}
+
+func (h Header) Empty() bool {
+	return h.tableHeader == nil
+}
+
+func (h Header) Node() ast.Node {
+	if h.Empty() {
+		return ast.NewText()
+	}
+	return *h.tableHeader
+}

internal/song/song.go

@@ -22,35 +22,3 @@ func (s Song) RemoveColumns(idx Indexes) Song {
 	s.TableRow = RemoveCols(idx, s.TableRow)
 	return s
 }
-
-type Header struct {
-	tableHeader *ast.Node
-}
-
-func NewHeader(h *ast.Node) Header {
-	return Header{tableHeader: h}
-}
-
-func (h Header) Remove() Header {
-	h.tableHeader = nil
-	return h
-}
-
-func (h Header) RemoveColumns(idx Indexes) Header {
-	if !h.Empty() {
-		removed := RemoveCols(idx, *h.tableHeader)
-		h.tableHeader = &removed
-	}
-	return h
-}
-
-func (h Header) Empty() bool {
-	return h.tableHeader == nil
-}
-
-func (h Header) Node() ast.Node {
-	if h.Empty() {
-		return ast.NewText()
-	}
-	return *h.tableHeader
-}