Add newline to options "continue" and "prompt".
Neovim job is activated only by complete lines, but by default the
'continue' and 'prompt' strings do not include "\n" and, consequently
they go to a JobActivity only when R outputs something else that
includes a newline. To avoid this, we are creating special values for
the 'continue' and 'prompt' options, including a "\n", that Vim-R-plugin
can recognize and replace.
Remove newline from end of Neovim strings.
Also: replace "localhost" with "127.0.0.1".