* docs: `newGuest` in `WebContents` and `webContents` in `BrowsweWindow`
According to the example codes in the documentation of `new-window`
event in `WebContents`, `webContents` in `BrowsweWindow` constructor
options and `newGuest` in `event` argument of `new-window` handler are
both existing but documented. This patch is for adding the related
documentations. Also, it provides typescript-definitations for these
two properties.
* Remove the documnent of `webContents` in BrowserWindow constructor option.
