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

Suggested by G. Brandon Robinson.

man/man3/draw.3

@@ -259,7 +259,7 @@ The clipping region may be modified dynamically using
 .TP
 .B chan
 The pixel channel format descriptor, as described in
-.IM image (7) .
+.MR image (7) .
 The value should not be modified after the image is created.
 .TP
 .B depth
@@ -268,7 +268,7 @@ number of bits per pixel in the picture;
 it is identically
 .B chantodepth(chan)
 (see
-.IM graphics (3) )
+.MR graphics (3) )
 and is provided as a convenience.
 The value should not be modified after the image is created.
 .TP
@@ -712,7 +712,7 @@ what
 is to
 .B atan
 (see
-.IM sin (3) ).
+.MR sin (3) ).
 .TP
 .BI border( dst\fP,\fP\ r\fP,\fP\ i\fP,\fP\ color\fP,\fP\ sp\fP)
 .I Border
@@ -810,11 +810,11 @@ is non-zero.
 .SH SOURCE
 .B \*9/src/libdraw
 .SH SEE ALSO
-.IM graphics (3) ,
-.IM stringsize (3) ,
-.IM color (7) ,
-.IM utf (7) ,
-.IM addpt (3)
+.MR graphics (3) ,
+.MR stringsize (3) ,
+.MR color (7) ,
+.MR utf (7) ,
+.MR addpt (3)
 .PP
 T. Porter, T. Duff.
 ``Compositing Digital Images'',