parser: caption: allow trailing whitespace.

drop sanitize anchor name as it leads to underscores being changed to
dashes, which is suppresing.

Make the detection simpler and check if there is trailing whitespace,
which we allow.

Add test case in mmark repo.

Signed-off-by: Miek Gieben <miek@miek.nl>

parser/caption.go

@@ -17,7 +17,6 @@ func (p *Parser) caption(data, caption []byte) ([]byte, string, int) {
 
 	id, start := captionID(data)
 	if id != "" {
-		id = sanitizeAnchorName(id)
 		return data[:start], id, end + j
 	}
 
@@ -57,8 +56,14 @@ func captionID(data []byte) (string, int) {
 	}
 	for k = j + 1; k < end && data[k] != '}'; k++ {
 	}
-	// Must be at the ending, otherwise we will ignore it.
-	if j < end-4 && k == end-2 {
+	// remains must be whitespace.
+	for l := k + 1; l < end; l++ {
+		if !isSpace(data[l]) {
+			return "", 0
+		}
+	}
+
+	if j > 0 && k > 0 && j+2 < k {
 		return string(data[j+2 : k]), j
 	}
 	return "", 0