[The next major update] Change all things to be git-based

[mosop]

I decided to break and reduce the scope of this library and change all things to be git-based in the "interactive" mode.

In cases of the interactive mode, I think that most of people want to manage file changes in their repositories. That is a "what will be changed in my working tree?" issue.

So, I redefine the user's workflow in the interactive mode more simple. To see file changes, users use their favorite Git clients. And Teeplate will only ask users "some changes are found in your working tree. ok?"

Teeplate will do:

• Check working tree statuses and ask users whether Teeplate can change files ONE TIME each single rendering session, that includes multiple file changes
• Provide APIs to retrieve information about file changes

Teeplate will not do:

• Display diff
• Ask each file
• Display information about changes