Shortcut key bindings

[dhardy]

Issue: on X11, the calculator doesn't support some keyboard shortcuts, e.g. Asterisk for multiply and Return.

Also concerns Wayland: the key remapping situation is similar.

Blocker: rust-windowing/winit#1266

[dhardy]

#100 introduces several unicode → VirtualKeyCode mappings. Quite a few of the obvious bindings for ASCII chars are missing.

What this should do beyond ASCII isn't obvious: unicode is huge and quite a number of the characters could have one (or more) corresponding keys in VirtualKeyCode. This probably depends on what happens to VirtualKeyCode; watch the above-linked winit PR and the issues linked from that.

[dhardy]

This is not really an issue now (at least, the specific key bindings are fixed).

Winit will likely deprecate VirtualKeyCode entirely at some point. We don't need to track this here.