Tab auto-completion feature

[woojung3]

Can you add tab auto-completion feature to terminal.cpp, Term:prompt?

If one wants a tab auto-completion, the only possible way is copying terminal.cpp codes and add "case Key::TAB:" by oneself.
It would be nice if tab auto-completion is provided by default in prompt sample code.

[staxfur]

That's a nice idea. The prompt is mainly used by the lfortran compiler, which might have this already implemented. @certik can you port it from lfortran, or do we need to make a new implementation for that?