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.

strings.1

@@ -10,7 +10,11 @@
 .Sh DESCRIPTION
 .Nm
 prints the printable character sequences that are at least 6 characters
-long.  If no files are given then it uses stdin.
+long. If no
+.Ar files
+are given,
+.Nm
+reads from stdin.
 .Sh STANDARDS
 .Nm
 mirrors the semantics of Plan9