fix mandoc warnings

- sort references in SEE ALSO section to section number, name.
- cols.1: proper order of sections.
- wrap lines to max 79 column length.

expr.1

@@ -76,7 +76,8 @@ against
 is anchored with an implicit '^'.
 .Pp
 You can't directly match the empty string, since zero matched characters
-resolve equally to a failed match. To work around this limitation, use "expr X'' : 'X$' instead of "expr '' : '$'"
+resolve equally to a failed match. To work around this limitation, use
+"expr X'' : 'X$' instead of "expr '' : '$'"
 .El
 .Sh EXIT STATUS
 .Bl -tag -width Ds