Added case for window resize

In the current version, Starting in a smaller than window sized terminal would cause word wrapping. The only way to fix it was to stop, resize the window and then restart cursynth.

Adding in the case for KEY_RESIZE in the TextInput(int) will allow the redrawing of the screen as the terminal size changes.

Supporting functions in cursynth.cpp and cursynth_gui.cpp were need to prevent the killing and recreation of the window, but instead clearing the window and redrawing all of the controls.