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

Add description of new libmach.
diff --git a/man/man3/stringsize.3 b/man/man3/stringsize.3
index 3ae2823..0e4e3ca 100644
--- a/man/man3/stringsize.3
+++ b/man/man3/stringsize.3
@@ -57,10 +57,10 @@
 .SH SOURCE
 .B /sys/src/libdraw
 .SH "SEE ALSO"
-.IR addpt (2),
-.IR cachechars (2),
-.IR subfont (2),
-.IR draw (2),
+.IR addpt (3),
+.IR cachechars (3),
+.IR subfont (3),
+.IR draw (3),
 .IR draw (3),
 .IR image (6),
 .IR font (6)