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

Add description of new libmach.
diff --git a/man/man3/regexp.3 b/man/man3/regexp.3
index 13c974c..d332cdd 100644
--- a/man/man3/regexp.3
+++ b/man/man3/regexp.3
@@ -42,7 +42,7 @@
 regular expression and returns
 a pointer to the generated description.
 The space is allocated by
-.IR malloc (2)
+.IR malloc (3)
 and may be released by
 .IR free .
 Regular expressions are exactly as in