This is a very first attempt at enabling neovim support for
vim-taskwarrir. In my use the only functions that require interaction
are undo and delete, for these two functions there is a check
`has('nvim')` which changes execution from `!` to `terminal`. There is
also no `taskwarrior#refresh()` call, which is done in a BufEnter
autocmd.

The refresh of the terminal occurred before sync had updated so any new
tasks were not showing up when syncing in neovim.

All the conditionals in the check for nvim have been modified to check
for the positive rather than negative.

I am creating a new window every time there is a call to terminal, as
without it when there are multiple windows or tabs open the terminal
call will close the current window.