Add the "role" attribute from ARIA

https://www.w3.org/TR/wai-aria/#host_general_role

kcgihtml.c

@@ -470,6 +470,7 @@ static	const char *const attrs[KATTR__MAX] = {
 	"required", /* KATTR_REQUIRED */
 	"rev", /* KATTR_REV */
 	"reversed", /* KATTR_REVERSED */
+	"role", /* KATTR_ROLE */
 	"rows", /* KATTR_ROWS */
 	"rowspan", /* KATTR_ROWSPAN */
 	"sandbox", /* KATTR_SANDBOX */

kcgihtml.h

@@ -333,6 +333,7 @@ enum	kattr {
 	KATTR_REQUIRED,
 	KATTR_REV,
 	KATTR_REVERSED,
+	KATTR_ROLE,
 	KATTR_ROWS,
 	KATTR_ROWSPAN,
 	KATTR_SANDBOX,