egui_glium: add support for transparent windows

Also support non-decorated windows (without border)

egui_glium/CHANGELOG.md

@@ -9,18 +9,15 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 
 ## 0.10.0 - 2021-02-28
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 * [Add shaders for GLSL 1.2, GLSL ES 1.0 and 3.0](https://github.com/emilk/egui/pull/187)
   - now `egui` works well on old hardware which supports OpenGL 2.1 only like Raspberry Pi 1 and Zero.
 
 
 ## 0.9.0 - 2021-02-07
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 * Nothing new
 
 
 ## 0.8.0 - 2021-01-17
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 ### Fixed 🐛
 
 * Fix a bug where key releases weren't sent to egui
@@ -28,39 +25,31 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 
 ## 0.7.0 - 2021-01-04
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 ### Changed
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 * `http` `persistence` and `time` are now optional (and opt-in) features.
 
 
 ## 0.6.0 - 2020-12-26
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 ### Added
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 * `egui_glium` will auto-save your app state every 30 seconds.
 * `egui_glium` can now set windows as fixed size (e.g. the user can't resize the window). See `egui::App::is_resizable()`.
 
 ### Changed
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 * `egui_glium` will now save you app state to [a better directory](https://docs.rs/directories-next/2.0.0/directories_next/struct.ProjectDirs.html#method.data_dir).
 * `egui_glium::run`: the parameter `app` now has signature `Box<dyn App>` (you need to add `Box::new(app)` to your code).
 * Window title is now passed via the `trait` function `egui::App::name()`.
 
 ### Fixed 🐛
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 * Serialize window size in logical points instead of physical pixels.
 * Window position is now restored on restart.
 
+
 ## 0.5.0 - 2020-12-13
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 ### Changed
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 * FileStorage::from_path now takes `Into<Path>` instead of `String`
 
 
 ## 0.4.0 - 2020-11-28
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 Started changelog. Features:
 
 * Input