all: implement macro "footnote:"

Macro footnote grammar,

----
"footnote:" [ REF_ID ] "[" STRING "]"
----

In asciidoctor, footnote can be placed anywhere, even after WORD without
space in between.

The REF_ID, define the unique ID for footnote and can be used to reference
the previous footnote.
The first footnote with REF_ID, should have the STRING defined.
The next footnote with the same REF_ID, should not have the STRING
defined; if its defined, the STRING is ignored.

1 files changed, 3 insertions, 0 deletions

diff --git a/element.go b/element.go
index a558055..1abba9e 100644
--- a/element.go
+++ b/element.go
@@ -831,6 +831,9 @@ func (el *element) toHTML(doc *Document, w io.Writer) {
 		}
 		fmt.Fprintf(w, `<a href="#%s">%s</a>`, href, label)
 
+	case elKindFootnote:
+		htmlWriteFootnote(el, w)
+
 	case elKindMacroTOC:
 		if doc.tocIsEnabled && doc.tocPosition == metaValueMacro {
 			doc.tocHTML(w)