Release process

Since gtk-rs has multiple crates which have inter-dependencies, it's a bit painful to make a new release. So here are the multiple steps:

Merge master branch into crate branch in every repository (starting with sys and ending with gtk). (/!\ cairo-sys is in cairo repository, not sys /!)
Update crate version in Cargo.toml and the number of its gtk-rs dependencies.
Open pull requests to crate branches to corresponding repositories.
Once pull requests have been merged, publish all crates to crates.io (using the cargo publish command).
Merge pending branch into master in the gtk-rs/examples repository (by opening a pull request of course).
Update badges version number in the _data/crates.json in the gtk-rs/gtk-rs.github.io repository.
Write a blog post (add the file into _posts folder in gtk-rs.github.io repository) announcing the new release.
Update crate version of the master branches on every repository.

NOTE: Pull requests on the crate branch aren't build.