* feat: allow setting window shape
This binds Widget::SetShape, an API that already exists in Chromium (for
Windows and Linux). It's a more reliable method of having some parts of
your window be "click-through" than the current `setIgnoreMouseEvents`
API, which messes around with the `WS_EX_LAYERED` window style on
Windows, causing strange bugs and incompatibility with hardware
acceleration.
* update docs
* Add atom::api::TopLevelWindow
* Make BrowserWindow inherit TopLevelWindow
* Fix reading from wrong weak map
* Read options after setting content view
* OnWindowClosed is not guarenteed to run now
* Fix the offscreen hack in BrowserWindow
* Fix building on Linux
* Fix tests on Linux
* Fix building on Windows
