all: add support for document attribute "last-update-label"

By default the last-update-label value set to "Last updated" and the
value is the document modification time.

If the label is suppressed with "!", no "Last updated" will be print
on the footer.

1 files changed, 7 insertions, 5 deletions

diff --git a/attribute_entry.go b/attribute_entry.go
index a4dd722..c1d329f 100644
--- a/attribute_entry.go
+++ b/attribute_entry.go
@@ -11,11 +11,13 @@ type AttributeEntry map[string]string
 
 func newAttributeEntry() AttributeEntry {
 	return AttributeEntry{
-		MetaNameGenerator:    `asciidoctor-go ` + Version,
-		metaNameSectIDs:      ``,
-		metaNameShowTitle:    ``,
-		metaNameTableCaption: ``,
-		metaNameVersionLabel: ``,
+		MetaNameGenerator:       `asciidoctor-go ` + Version,
+		metaNameLastUpdateLabel: `Last updated`,
+		metaNameLastUpdateValue: ``,
+		metaNameSectIDs:         ``,
+		metaNameShowTitle:       ``,
+		metaNameTableCaption:    ``,
+		metaNameVersionLabel:    ``,
 	}
 }