Only show first 80 characters of commit subject in log and summary

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.h

@@ -73,6 +73,7 @@ extern char *fmt(const char *format,...);
 extern void html(const char *txt);
 extern void htmlf(const char *format,...);
 extern void html_txt(char *txt);
+extern void html_ntxt(int len, char *txt);
 extern void html_attr(char *txt);
 extern void html_link_open(char *url, char *title, char *class);
 extern void html_link_close(void);