Add additional numpad key mappings (#805)

* Add additional numpad key mappings

Since some platforms have already used the existing `Add`, `Subtract`
and `Divide` codes to map numpad keys, the X11 and Wayland platform has
been updated to achieve parity between platforms. On macOS only the
`Subtract` numpad key had to be added.

Since the numpad key is different from the normal keys, an alternative
option would be to add new `NumpadAdd`, `NumpadSubtract` and
`NumpadDivide` actions, however I think in this case it should be fine
to map them to the same virtual key code.

* Add Numpad PageUp/Down, Home and End on Wayland

src/platform_impl/macos/event_loop.rs

@@ -683,6 +683,7 @@ pub fn scancode_to_keycode(code: c_ushort) -> Option<events::VirtualKeyCode> {
         0x4a => events::VirtualKeyCode::VolumeDown,
         0x4b => events::VirtualKeyCode::Divide,
         0x4c => events::VirtualKeyCode::NumpadEnter,
+        0x4e => events::VirtualKeyCode::Subtract,
         //0x4d => unkown,
         0x4e => events::VirtualKeyCode::Subtract,
         0x4f => events::VirtualKeyCode::F18,