Salvaging 20 years of ruby/tk history

[amatsuda]

(As I told @hsbt in person before,) I really hate the way this repo treats the commits from the original repo.

8513179 squashes all 20 years of history of ruby/tk development in just one meaningless commit,
which seems totally disrespectful to the original authors (especially Nagai-sensei), and makes it impossible to code readers to go back through the history and understand the intension behind the code.

So, I salvaged all 700+ tk related commits back to @matz's very first 2e1501d from the original ruby repository.
You can now follow every single change for each file with git log --follow.
git blame everywhere on this repo now shows us what we expect.

Please note that this PR can't just be merged. What I'd suggest to do with this repo is to abandon the current master branch and force-push this branch as the master branch here, just like I & @mrkn did to https://github.com/ruby/bigdecimal repo.

Those who already cloned this repo may be a little bit confused, but I guess it wouldn't cause a big problem because I guess not that much people will be affected (there're only 2 forks so far, including mine), and it might not be very difficult to switch to the new master (just discard the old master and git pull).

[hsbt]

@amatsuda Thanks! I create tk team and added you to this team. Can you rewrite current master branch with this changes?

[amatsuda]

@hsbt Done!