Rewrite page(2) references to page(3).

Add description of new libmach.
diff --git a/man/man3/atof.3 b/man/man3/atof.3
index 9f7e775..2ab2f3f 100644
--- a/man/man3/atof.3
+++ b/man/man3/atof.3
@@ -129,7 +129,7 @@
 .SH SOURCE
 .B /sys/src/libc/port
 .SH SEE ALSO
-.IR fscanf (2)
+.IR fscanf (3)
 .SH DIAGNOSTICS
 Zero is returned if the beginning of the input string is not
 interpretable as a number; even in this case,