Re-organize and improve help command and help info for each command

libexec/tmuxifier-current-session

@@ -2,6 +2,14 @@
 set -e
 [ -n "$TMUXIFIER_DEBUG" ] && set -x
 
+# Provide tmuxifier help
+if [ "$1" == "--help" ]; then
+  echo "usage: tmuxifier current-session
+
+Outputs the name of the current Tmux session."
+  exit
+fi
+
 if [ -n "$TMUX" ]; then
   for item in $(tmux list-pane -F "#{session_name}");do
     echo $item