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

Add description of new libmach.
diff --git a/man/man3/encode.3 b/man/man3/encode.3
index f101b27..c756b27 100644
--- a/man/man3/encode.3
+++ b/man/man3/encode.3
@@ -49,9 +49,9 @@
 .PP
 .I Encodefmt
 can be used with
-.IR fmtinstall (2)
+.IR fmtinstall (3)
 and
-.IR print (2)
+.IR print (3)
 to print encoded representations of byte arrays.
 The verbs are
 .TP