This adds a completion source for [coc.nvim][coc] that autocompletes email
addresses for `ft=mail` buffers using [khard][khard].

## installation (vim-plug)

```
Plug 'lonkaars/coc-khard'
```

[coc]: https://github.com/neoclide/coc.nvim
[khard]: https://github.com/lucc/khard