New features for tabbar-ruler

Hello again,

I wrote 2 new features to tabbar-ruler:

(1) Provide new grouping mode:

When using tabbar-ruler, I usually opened many files in different types, so it is quite take time to switch buffer in tabbar-ruller because I need to switch group first. Hence, in this new group I place all user's files into a group and all emacs's buffers will be grouped into another group.

Note that I run my new group mode by default, so please change it if you want.

(2) Allow drag-and-drop feature in tabbar:

This feature allows user to reorder the opened buffers in tabbar using his mouse. I find out it is quite convenient for me when I open many buffers and want to place related ones near each others.

There's one point that I try to do but haven't done: I want to open the clicked buffer (in case that it isn't selected) before dragging it. My temporary solution is to open it after dropping, not really nice.
If you have time or know how to do it, please tell me. I'll be pleased to discuss more on that.

Best reagards,
Trung.