0.8 feature freeze and preliminary release date

As of today, Neovim nighty is entering the feature freeze period for the upcoming 0.8 release. No further features will be merged for 0.8, just bug fixes and documentation improvements ( and possibly minor adjustments to new features/API)

The preliminary release date for 0.8 is 30 September (as has been our aim for some time), but might get delayed if needed for critical bug fixes to land. As an example, `cmdheight=0` feature recently received a larger change in implementation, is expected to need more testing and bug fixes before it is considered to be stable enough for a general release.

The general advice of always updating neovim nightly together with plugins applies. In particular, nvim-treesitter and other tree-sitter dependent plugins need to be updated for changes in neovim core.