Opt-in to macOS Mojave Dark Mode

macOS 10.14 will bring a new system wide dark mode. To enable this, the
[official guides][] suggest to relink using the newest OS. This
approach, however, did not work for me as described in [an issue][] in
the glutin repository.

As a second option, the accompanying `Info.plist` file can also
overwrite the link-time check and enable dark mode rendering if the
system config is set by setting `NSRequiresAquaSystemAppearance` to
`YES`. This approach seems to work flawlessly no matter if a user opts
into dark mode or not.

I would appreciate it if someone can test this on macOS 10.13 as well,
but I suppose the key there is unused and would not break anything.

[official guides]: https://developer.apple.com/documentation/appkit/appkit_release_notes_for_macos_10.14_beta
[an issue]: https://github.com/tomaka/glutin/issues/1053#issuecomment-409315461

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Add support for macOS systemwide dark mode
 - Set the environment variable `COLORTERM="truecolor"` to advertise 24-bit color support
 
 ### Changed

assets/osx/Alacritty.app/Contents/Info.plist

@@ -32,5 +32,7 @@
   <true/>
   <key>CFBundleDisplayName</key>
   <string>Alacritty</string>
+  <key>NSRequiresAquaSystemAppearance</key>
+  <string>NO</string>
 </dict>
 </plist>