Figure out optimal strategy for version control

[novusnota]

For users to be able to specify dev/nightly/main for the latest updates and stable/release (or a particular Tact version tag). Then, update all the plugin configurations in the README.md and in docs, when they arrive in #7.

Otherwise, everyone's going to get the dev Tact syntax, which is ahead of the released ones, because I plan on keeping all the editor integrations of my creation (this one, soon-to-be-made Sublime Text package, and possibly others) and tree-sitter-tact in sync with the main branch of Tact compiler.

UPD: Consider adding a message on start-up if the flag let g:tact_prefer_legacy is not set — "Tact.vim was drastically updated and integrated with an LSP. Please, refer to instructions in README.md on https://github.com/tact-lang/tact.vim"

P.S.: just do semver releases?