Missing ImGUI controls

[afshinpir]

Some controls are not rendered correctly in ImTUI. Here are some some obvious ones:

• Separator
• Spacing
• Password InputText flag has no effect

I wish you could add support for these controls too. I guess the problem comes from how these elements are rendered.

[dufferzafar]

Also, I think context menus seem to be missing as well!

[davidchisnall]

The highlight for selected controls (if you enable keyboard navigation) is also probably not correct. It renders a two-character-wide box around the control, which causes a lot of visual corruption in the example.