Improve parse-section-in-parentheses

Recognize "foo(3scm)." in addition to "foo(3scm),"

scm/html/man.scm

@@ -162,16 +162,21 @@
     (format #f "<a href=\"~a\">~a</a>" url body)))
 
 (define (parse-section-in-parentheses str)
+  (define (is i choices)
+    (let ((char (string-ref str i)))
+      (let loop ((k 0))
+        (and (< k (string-length choices))
+             (or (char=? char (string-ref choices k))
+                 (loop (+ k 1)))))))
   (let* ((n (string-length str))
          (r (and (>= n 3)
-                 (char=? #\( (string-ref str 0))
-                 (char<=? #\1 (string-ref str 1))
-                 (char<=? (string-ref str 1) #\9)
-                 (cond ((char=? #\) (string-ref str (- n 1)))
+                 (is 0 "(")
+                 (is 1 "123456789")
+                 (cond ((is (- n 1) ")")
                         1)
                        ((and (>= n 4)
-                             (char=? #\) (string-ref str (- n 2)))
-                             (char=? #\, (string-ref str (- n 1))))
+                             (is (- n 2) ")")
+                             (is (- n 1) ",."))
                         2)
                        (else
                         #f)))))