Added support to execute in NeoVim :terminal

[brodock]

NeoVim has it's own terminal emulator without requiring additional vim-scripts, see: https://www.youtube.com/watch?v=xZbMVj9XSUo

Fix #72

[styx]

@brodock thanks for the addition. At first you should update docs to get this merged.

[styx]

Add docs for g:vroom_use_terminal

[brodock]

@styx I've added g:vroom_use_terminal documentation and made a few more fixes/improvements in the way NeoTerminal will open a split window and handle multiple execution of the same file:

• It reuses the same split at current tab
• As we can't re-use the terminal buffer, we have to close the old one and open a new
• As terminal buffer name colide with the Regexp to identify if it's a spec file or not, additional checks are made to be sure current buffer is not NeoVim terminal
• With changes above you can <leader>\r even when Terminal is focused and get expected results

[styx]

Looks good to me, just may be g:vroom_use_terminal should be g:vroom_use_nvim_terminal.
Let's wait for @skalnik, might be he want to take a look too.

[skalnik]

Seems reasonable to me! ❤️ 👍

I'm a bit indifferent about changing this to include nvim or neovim in the flag since normal vanilla Vim (vimilla?!) doesn't really have good terminal support. If it eventually does gain this, we can alter the settings as we need to.