Windows creates Alt event instead of Menu event. (to match other platforms)

[rukai]

Fixes #549

LMenu + RMenu is from the original batch of events copied from some windows list by tomaka 24baf4d
While LAlt + RAlt were added later. f86af01

Because LAlt + RAlt is used on every other platform, and its a better description, I propose we delete LMenu + RMenu and point the windows key events LMenu + RMenu to LAlt + RAlt instead.

State of other platforms:

• x11 uses LAlt + RAlt https://github.com/tomaka/winit/blob/master/src/platform/linux/x11/events.rs#L168
• wayland uses LAlt + RAlt https://github.com/tomaka/winit/blob/master/src/platform/linux/wayland/keyboard.rs#L247
• empscripton uses LAlt + RAlt https://github.com/tomaka/winit/blob/master/src/platform/emscripten/mod.rs#L637
• mac os looks looks like it isnt implemented? https://github.com/tomaka/winit/blob/master/src/platform/macos/events_loop.rs#L605 whatever the case, I shouldnt touch mac os as I dont have access to a machine to test on.
• android doesn't use VirtualKeyCode
• ios doesn't use VirtualKeyCode

[francesca64]

Thanks! This looks like a thorough investigation, and I'm definitely in favor of this change.

mac os looks looks like it isnt implemented?

Ha, that would explain why I get virtual_keycode: None when pressing the alt key on macOS. I'm surprised I never noticed. I'll tack a quick fix for that onto this, if you don't mind.

[francesca64]

I just remembered that I'm not supposed to merge a breaking change before the 0.15.1 release, so this will have to wait until after I fix a few more bugs.

[francesca64]

...RWin and LWin are also swapped on macOS. Don't tell anyone this, but I have a lot of trouble distinguishing left from right.