tmac: rename IM (italic manual) to MR (manual reference)

Suggested by G. Brandon Robinson.

man/man3/rand.3

@@ -125,7 +125,7 @@ truly random bytes read from
 .PP
 .I Prng
 uses the native
-.IM rand (3)
+.MR 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
-.IM mp (3) ).
+.MR mp (3) ).
 .PP
 .I Fastrand
 uses
@@ -161,7 +161,7 @@ to return a uniform
 .B \*9/src/libsec/port
 .SH "SEE ALSO
 .\" .IR cons (3),
-.IM mp (3)
+.MR mp (3)
 .SH BUGS
 .I Truerand
 and
@@ -181,7 +181,7 @@ are preprocessor macros defined as
 .IR p9lrand ,
 and so on;
 see
-.IM intro (3) .
+.MR intro (3) .
 .ie \n(HT .ds HT "
 .el .ds HT " (see HTML-formatted man page for link)
 .PP