WebKitGTK+ 2.21.2 released!

This is a development release leading toward 2.22 series.

Remove resource load statistics API, it’s not ready yet.
Add initial implementation of WebDriver advance user insteraction commands.
Add introspectable alternatives for functions using vargars to JavaScriptCore GLib API.
Implement MouseEvent.buttons.
Do TLS error checking on GTlsConnection::accept-certificate to finish the load earlier in case of errors.
Fix downloads started by context menu failing in some websites due to missing user agent HTTP header.
Avoid painting backing stores for zero-opacity layers.
Fix the installation path of API documentation.
Fix several crashes and rendering issues.

Thanks to all the contributors who made possible this release.