This is the first "release" of vimtex. Versioning has not been a priority, as I have mostly avoided breaking changes. However, as discussed in #1748, I have decided to adapt more recent features in Vim and neovim. This means that users on older versions of Vim may experience that vimtex stops working. Thus, I want to apply versioning to make it easy to pin the version if one is stuck on old versions of Vim or neovim.
In future releases I plan to write more about the changes since the last release. Since this is the first release, one should simply all of the docs. :)