Version have the following syntax: <M>[.<m>[.<U>[-<extra>]]]
Major changes made / product completed.
On libraries, it means completely incompatible API with the previous version.
Minor changes made.
On libraries, it means new major features have been added, but API should remain compatible.
Only bugfixes or very minor features.
May match a Git tag done before a big change (for instance: before switching from Gtk 2 to Gtk 3).
If extra == "git", indicates a version directly taken from the git repository.