Add support for treemacs

[Alexander-Miller]

Updated treemacs PR, as requested in #2.

[tarsius]

Thanks!

Because I don't use this package, I cannot actually test this, but it looks obviously right, so I am merging it.

(Well, I would have merged, but I also wanted to add #4 to the commit message, and wasn't able to push to your feature branch, so this is now "merged".)

[Alexander-Miller]

Turns out the code isn't quire correct - I assumed evil-escape would use the motion-state path because that's what treemacs-state inherits from, but the treemacs code needs to go into the normal state path instead. I'll open a new PR in a few minutes.

It'll also require an up-to-date version of treemacs since I added treemacs to evil-escape-excluded-major-modes a while ago. I can't remember exactly what was incompatible, but now that official support is added I'll remove this part again.

Well, I would have merged, but I also wanted to add #4 to the commit message, and wasn't able to push to your feature branch, so this is now "merged"

Sorry, I could've sworn I had checked the allow edits option. No idea why it's disabled now.