better and more predication, improved documentation

test/stralloc_buffer.c

@@ -3,6 +3,8 @@
 
 main() {
   static stralloc sa;
+  /* static makes sure sa is initialized and empty;
+   * use stralloc_init to initialize and stralloc_copys(&sa,"") to empty */
   if (buffer_get_token_sa(buffer_0,&sa," \t\n",3)==0) {
     buffer_putsa(buffer_1,&sa);
     buffer_putnlflush(buffer_1);