Support show multiple commits as one diff view

[watergear]

Sometimes we need to review series of commits from someone in a period of time.

We have to do such like:

1. Show each commit one by one in a period of time.
   E.g
   run Git: View Commits from Selected Lines, and then multiple commits are showed in indiviual views.

2. Show total difference between two commits at the begin and end time.
   E.g
   press Alt+` and run diff start end, and then one commit is showed in panel view.

But there are maybe some unexpected difference (do not from the specific commits) are show to us.
The hello2.txt is unexpected for us.

---

Need to provide a command to show all difference as only ONE diff view from specific commits.
We suppose to see: