use tmux on shell start

.zsh.d/40-always-tmux.zsh

@@ -0,0 +1,11 @@
+if [[ "$TERM" == screen* ]] || [[ -n "$TMUX" ]]; then
+  return 1
+fi
+
+if tmux list-sessions && (tmux list-sessions | test -n "$0"); then
+  session_id=`date +%Y%m%d%H%M%S`
+  tmux new-session -d -t base -s $session_id
+  tmux attach-session -t $session_id \; set-option destroy-unattached
+else
+  tmux new-session -s base
+fi