add some mandoc pages and fix some warnings

- add .Os, it is mandatory.
- don't redeclare .Nm when it's not needed.
- fix some warnings (checked with mandoc -Tlint).
- remove some leftover old stuff.

chgrp.1

@@ -1,22 +1,28 @@
-.TH CHGRP 1 sbase\-VERSION
-.SH NAME
-chgrp \- change the file group ownership
-.SH SYNOPSIS
-.B chgrp
-.RB [ \-R ]
-.I groupname
-.I file...
-.SH DESCRIPTION
-.B chgrp
+.Dd January 30, 2015
+.Dt CHGRP 1 sbase\-VERSION
+.Os
+.Sh NAME
+.Nm chgrp
+.Nd change the file group ownership
+.Sh SYNOPSIS
+.Nm
+.Op Fl R
+.Ar groupname
+.Op Ar file...
+.Sh DESCRIPTION
+.Nm
 sets the group id of the files specified by
-.IR file
+.Ar file
 to the gid of the group named
-.IR group.
+.Ar group.
 If the
-.IR R
+.Fl R
 flag is specified, this process is recursively applied to
 everything in
-.IR file.
-
-.SH SEE ALSO
-.IR chown (1) chown (2) chmod (1) chmod (2) getgrnam (3)
+.Ar file .
+.Sh SEE ALSO
+.Xr chown 1 ,
+.Xr chown 2 ,
+.Xr chmod 1 ,
+.Xr chmod 2 ,
+.Xr getgrnam 3