Update newer XDG_CONFIG/tmux.conf to be like ~/.tmux.conf

I should eventually remove the older ~/.tmux.conf, but until all my
systems are on the latest tmux I have to sync like this.

private_dot_config/tmux/tmux.conf

@@ -0,0 +1,21 @@
+set-option -g default-shell /usr/bin/fish
+
+bind-key h select-pane -L
+bind-key j select-pane -D
+bind-key k select-pane -U
+bind-key l select-pane -R
+
+# nested tmux, obey me
+bind-key a send-prefix
+
+# Avoid the annoying bit of delay when using the control character
+set -g escape-time 0
+set -g renumber-windows on
+
+# Show a visual bell, even on other windows
+set-window-option -g visual-bell both
+set-window-option -g bell-action other
+
+# Set up the window visuals
+set -g window-status-style bg=yellow
+set -g window-status-current-style bg=red,fg=white