Add docstrings

src/url.c

@@ -4,7 +4,7 @@ struct url {
   size_t key, user, pass, host, port, uri, end;
 };
 
-int mg_url_is_ssl(const char *url) {
+bool mg_url_is_ssl(const char *url) {
   return strncmp(url, "wss:", 4) == 0 || strncmp(url, "https:", 6) == 0 ||
          strncmp(url, "mqtts:", 6) == 0 || strncmp(url, "ssl:", 4) == 0 ||
          strncmp(url, "tls:", 4) == 0 || strncmp(url, "tcps:", 5) == 0;