Hi Yuan!

I've make some changes to my *-ts-modes, and would appreciate a second
opinion as well as a push to the feature/tree-sitter branch :-)

I've extracted some of the relevant mode-init variables into defcustoms
so that users can tweak their behavior.  It also seems I forgot some
electric indent configs in some of the other files, so I added that
aswell.

BTW, should we do the same thing we did with js-mode - add a js-ts-mode
and don't change the js.el file at all?  We could either go the same
route as c-ts-mode, where we define both c and c++ in the same file, or
keep them separate.  What do you think?

Theo