Make minor improvements

libc/str/ispunct.c

@@ -19,6 +19,9 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/str/str.h"
 
+/**
+ * Returns nonzero if c ∈ !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
+ */
 int ispunct(int c) {
   return (0x21 <= c && c <= 0x7E) && !('0' <= c && c <= '9') &&
          !('A' <= c && c <= 'Z') && !('a' <= c && c <= 'z');