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

Add description of new libmach.

man/man3/rand.3

@@ -125,7 +125,7 @@ truly random bytes read from
 .PP
 .I Prng
 uses the native
-.IR rand (2)
+.IR rand (3)
 pseudo-random number generator to fill the buffer.  Used with
 .IR srand ,
 this function can produce a reproducible stream of pseudo random
@@ -138,7 +138,7 @@ and
 may be passed to
 .I mprand
 (see
-.IR mp (2)).
+.IR mp (3)).
 .PP
 .I Fastrand
 uses
@@ -167,7 +167,7 @@ to return a uniform
 .B /sys/src/libsec/port/*fastrand.c
 .SH "SEE ALSO
 .IR cons (3),
-.IR mp (2),
+.IR mp (3),
 .SH BUGS
 .I Truerand
 and