I port nanogui, but besides porting I'd like to improve it using great
capabilities of D language provides. One of them is utf support, so I
added support for Asian languages to nanogui.TextBox. But I'm not sure
I've did it well and so I'd like to ask someone to test it using the
following:
```
git clone --recursive https://github.com/drug007/nanogui.git
cd nanogui
git checkout textbox # TextBox exists in this branch only
dub --config=sdl # Keyboard events provided only by SDL2 backend only
```
On the right side there will be a window with four text boxes with
russian, english, japanese and chinese text respectively. It would be
nice to get some feedback from users - probably I did something totally
wrong. Also I'm curious does it worth efforts?
