toxcore-git: use sha256sums
Added msgpack-c-git PKGBUILD
neovim-git: update PKGBUILD

- Removed install script; its statement was obvious
- Go back to using regular msgpack, and msgpack-c at that
- Removed 'vim-runtime' from optdepends; Vim's runtime has since been
  reintegrated into nvim.
- md5sums -> sha256sums
Misc. cleanup everywhere
Added lua-messagepack-git