Tweaks requested by Baron, plus fixes.

Tweaks:
* --headers command line option, which can be used to
        enable/disable the automatic headers, and the
        automatic empty lines between samples.
* --show-timestamps, which changes the #ts line with
        a timestamp in the HH:MM:SS format.
* Always use ReadKeyMini, even when we have Term::ReadKey.
        In the latter case, use the Term::ReadKey functions,
        but if they fail, try again with our own versions.

Fix:
Looks like I forgot to actually enable the "save the current, first
and last" samples. This is now on. It should mean faster and better
output when changing --group-by modes.

lib/ReadKeyMini.pm

@@ -48,7 +48,18 @@ BEGIN {
    my $have_readkey = eval { require Term::ReadKey };
 
    if ($have_readkey) {
-      Term::ReadKey->import(@EXPORT_OK);
+      *ReadMode = sub {
+         eval { return Term::ReadKey::ReadMode( @_ ) };
+         if ( $@ ) {
+            return _ReadMode(@_);
+         }
+      };
+      *GetTerminalSize = sub {
+         eval { return Term::ReadKey::GetTerminalSize( @_ ) };
+         if ( $@ ) {
+            return _GetTerminalSize(@_);
+         }
+      };
    }
    else {
       # If we don't have Term::ReadKey, fake it. We clobber our own glob,