- Automatic VT allocation mechanism is implemented. 
  Since U++ suppports function keys from F1 to F12, I have limited the valid VT numbers within tty1-tty12 range (This can be easily changed if required).

- Accordingly, VT switching is implemented.
  Since we mute the vt keyboard input, this required manual handling of the linux signals, and as a result the vt handle had to be made a global static integeer (atomic).

- To prevent any screen buffer damage, U++ linuxframebuffer backend now does not copy the drawn image onto framebuffer when the
  vt is switched away (i,e., whem it loses focus).

- Accordingly, CTRL + ALT + [F1-f12] key combinations are reserved for VT switching.

- SHIFT keys are not working properly. (Can't get any capital letters.)

- No double click.

- No key repeat.